Tool and Die Maker Apprentice Training

From metal processing and grinding to forging and manufacturing, the Tool and Die Maker Apprentice Training curriculum offers a complete introduction for the professional tool and die maker.

Beginning with a systematic review of pre-technical skills in safety, drawings, and measurements, the curriculum takes students, step by step, through the fundamentals of tool grinding, metallurgy, and the manufacturing process.

Like many Penn Foster apprentice programs, this Machinist/Machinist Apprentice has been developed to meet Bureau of Apprenticeship and Training (BAT) standards. Be sure to offer your employees on-the-job training opportunities to supplement the skills learned here. Upon completion of this program, students will be able to:

Read working drawings.

Identify different types of cutting tools.

Explain the function of forming dies.

Select the proper machine tool for a job.

Explain how to recognize steel alloys.

Explain the use of a fixture.

Explain the function of forging dies.

Describe a layout procedure.

Discuss the hardening and tempering of steels.

Explain the various uses of a jig.

Discuss the use of drill bushings.

Explain how to lay out a casting.

Describe various press operations.

Career Advice on How to Become a Tool and Die Maker

Tool and die makers are among the most skilled of all tradesmen. The typical tool and die maker builds other tools that are then used in the manufacturing process. The tools which a tool and die maker creates are used to form metal into different shapes, whether this is done through cutting or bending. 

A die is a metal form that is used to shape metal, but tool and die makers also make molds as well. These molds can be used to produce parts made of almost any material, ranging from plastic to even composite materials. Due to the nature of the work, tool and die makers frequently work with engineers and need to have a detailed knowledge of machine operation, as well as an ability to read blueprints.

Career Facts:

Those engaged in career planning realize that tool and die makers often have several years of classroom training, usually at least four years. This training is in addition to their apprenticeships and additional course work often at technical schools. Tool and die makers with a college degree can also venture into engineering or tool design. The numbers for this skilled position are expected to decline.

Career Opportunities and Job Outlook-Fair:

While this occupation may be very skilled, there is an expected decrease in their numbers. In 2006, there were 101,000 tool and die makers. As of 2016, that number is expected to contract considerably to 91,000. This is a significant ten-percent reduction.  

On the plus side, however, because of the vital nature of their work for industry at large, the tool and die maker is more protected from layoffs than many other workers involved in manufacturing. However, the overall picture is complicated, as there are not enough projected skilled tool and die workers to meet the demand. The job search for those looking for a career in tool and die should be a fruitful one.

A Day in The Life:

Tool and die makers are highly skilled, and, as a result, are often able to bypass some of the more dangerous jobs in manufacturing. Traditionally, their skill sets are sought after by the manufacturing industry. Increasingly, they are using computers in their work. Tool and die makers need to know how to work with engineers and read blueprints. This is vital to their job, for without the ability to read blueprints, tool and die makers can simply not build the machines necessary.

Tool and die makers spend most of their day literally building machines or tools and dies from the ground up. The end result is a serious contribution to the manufacturing process.

Average Salary:

Despite the very high level of skill that the job requires, tool and die makers do not enjoy a pay that is reflective of their overall skill. On average a tool and die maker earns about $21 per hour, with the top ten-percent of earners seeing about $32 per hour.

$40k - $67k

Career Training and Qualifications:

Several years of technical training and apprenticeship is quite common for this career’s training. Additional training at technical schools and community colleges is likewise common. Due to the skill level involved, constant on the job training is also the norm.

Cold Saw

Portable saws

These saws were primarily designed for sheet metal roofers in the building industry. Cold saws, as opposed to abrasive saws, are used so that protective coating is not damaged. They also have a heavy duty aluminium catcher which is useful for capturing the swarf.

They can cut up to 6mm (0.24in) thick mild steel. They use cermet tipped blades.

Blades

Cold saw blades are circular metal cutting saw blades categorized into two types: solid HSS or tungsten carbide-tipped (TCT). Both types of blades are resharpenable and may be used many times before being discarded. Cold saw blades are used to cut metal using a relatively slow rotational speed, usually less than 5000 surface feet per minute (SFM) (25m/s), and a high chip load per tooth, usually between .001" - .003" (0.025 - 0.08mm) per tooth. These blades are driven by a high power motor and high-torque gear reduction unit or an AC vector drive. During the cutting process, the metal is released in a shearing action by the teeth as the blade turns and the feed mechanism moves the blade forward. They are called "cold saw blades" because they transfer all the energy and heat created during the cutting process to the chip. This enables the blade and the work material to remain cold.

Classification

The first type of cold saw blade, solid HSS, may be made from either M2 tool steel or M35 tool steel, alloyed with additional cobalt. Solid HSS saw blades are heat treated and hardened to 64/65 HRC for ferrous cutting applications and 58/60 HRC for non-ferrous cutting applications. This high hardness gives the cutting edges of the teeth a high resistance to heat and wear. However, this increased hardness also makes the blades brittle and not very resistant to shock. In order to produce a high quality HSS cold saw blade, you must start with very flat and properly tensioned raw material. The blades must be press quenched after hardening to prevent them from being warped. The term HSS doesn't necessarily mean what it implies. These blades are usually never run at surface speeds higher than 350 SFM. Solid HSS cold saw blades may be used for cutting many different shapes and types of metal including: tubes, extrusions, structural sections, billets, bars, ingots, castings, forgings etc. These blades may also be coated with special wear resistant coatings such as titanium nitride (TiN) or titanium aluminum nitride (TiAlN).

The second type of cold saw blade, tungsten carbide-tipped (TCT), are made with an alloy steel body and tungsten carbide inserts brazed to the tips of the teeth. These tips are ground on all surfaces to create tangential and radial clearance and provide the proper cutting and clearance angles on the teeth. The alloy body is generally made from a wear resistant material such as a chrome vanadium steel, heat treated to 38/42 HRC. The tungsten carbide tips are capable of operating at much higher temperatures than solid HSS, therefore, TCT saw blades are usually run at much higher surface speeds. This allows carbide-tipped blades to cut at faster rates and still maintain an acceptable chip load per tooth. These blades are commonly used for cutting non-ferrous alloys, but have gained significant popularity for ferrous metal cutting applications in the last 10 years. The tungsten carbide inserts are extremely hard (98 HRC) and capable of very long wear life. However, they are less resistant to shock than solid HSS cold saw blades. Any vibration during the cutting process may severely damage the teeth. These cold saw blades need to be driven by a backlash free gear box and a constant feed mechanism like a ball-screw feed.

Future

The popularity of cold saw blades is increasing due to the technological advancements in cold saw machines. They are the sawing method of choice when high production requirements are needed. They consistently produce the lowest cost per cut among all sawing methods: hot sawing, friction sawing, bandsawing and hacksawing.

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Metalworking

Tools

Cutting machines

Water jet cutter Band saw Cold saw Laser Miter saw Plasma

Cutting tools

Broach Burr Chisel Counterbore Countersink End mill File Guillotine shear Hand scraper Milling cutter Nibbler Reamer Throatless shear Tipped tool Tool bit

Forming tools

Brake Die English Wheel Flypress Hydraulic press Machine press Punch press Stamping press

Hand tools

Clamp Combination square Drift pin File card Hacksaw Hammer Hand scraper Machinist square Magnetic base Needlegun scaler Pipe and tube bender Pliers Punch Saw piercing Scriber Tap and die Tongs Vise Workbench Wrench

Machine tooling

Angle plate Chuck Collet Jig Fixture Indexing head Lathe center Machine taper Magnetic base Mandrel Rotary table Wiggler

Measuring instruments

Bore gauge Caliper Comparator Dial indicator Engineer's blue Feeler Center gauge and fishtail gauge Gauge block Gauge Go-NoGo Machinist square Marking blue Marking gauge Marking out Micrometer Radius gauge Scale Sine bar Spirit level Straightedge Surface plate Tape measure Thread pitch Height gauge Vernier scale Wiggler

Smithing tools

Anvil Forge Fuller Hardy hole Hardy tools Pritchel Slack tub Steam hammer Swage block Trip hammer

Casting Fabrication Forming Jewellery Machining Metallurgy Smithing Tools & Terminology Welding.

Tool

A tool is any physical item that can be used to achieve a goal, especially if the item is not consumed in the process. Informally the word is also used to describe a procedure or process with a specific purpose. Tool use by humans dates back millions of years, and other animals are also known to employ simple tools.

Tools that are used in particular fields or activities may have different designations such as "instrument", "utensil", "implement", "machine", or "apparatus". The set of tools needed to achieve a goal is "equipment". The knowledge of constructing, obtaining and using tools is technology.

History

Prehistoric stone tools over 10,000 years old, found in Les Combarelles cave, France

Carpentry tools recovered from the wreck of a 16th century sailing ship, the Mary Rose. From the top, a mallet, brace, plane, handle of a T-auger, handle of a gimlet, handle of a hammer?, rule.

Stone and metal knives

An upholstery regulator

Anthropologists believe that the use of tools was an important step in the evolution of mankind. Humans evolved an opposable thumb — useful in holding tools — and increased dramatically in intelligence, which aided in the use of tools. Because tools are used extensively by both humans and wild chimpanzees, it is widely assumed that the first routine use of tools took place prior to the divergence between the two species. These early tools, however, were likely made of perishable materials such as sticks, or consisted of unmodified stones that cannot be distinguished from other stones as tools. The beginning of the Stone Age marks the era when hominins first began manufacturing stone tools, and evidence of these tools dates back at least 2.6 million years in Ethiopia. One of the earliest distinguishable stone tool forms is the hand axe.

Up until recently, weapons found in digs were the only tools of “early man” that were studied and given importance. Now, more tools are recognized as culturally and historically relevant. As well as hunting, other activities required tools such as preparing food, “…nutting, leather working, grain harvesting and woodworking…” Included in this group are “flake stone tools (which may or may not have been used more commonly by women).” This recognition in other tools used by early people is attributed to the addition of feminist perspective in anthropology and archaeology.

Tools are the most important items that the ancient humans used to climb to the top of the food chain; by inventing tools, they were able to accomplish tasks that human bodies could not, such as using a spear or bow and arrow to kill prey, since their teeth were not sharp enough to pierce many animals' skins. “Man the hunter” as the catalyst for Hominin change has been questioned. Based on marks on the bones at archaeological sites, it is now more evident that pre-humans were scavenging off of other predator’s carcasses rather than killing their own food.

The transition from stone to metal tools roughly coincided with the development of agriculture. Mechanical devices experienced a major expansion in their use in Ancient Greece and Ancient Rome with the systematic employment of new energy sources.especially waterwheels. Their use expanded through the Dark Ages with the addition of windmills.

Machine tools occasioned a surge in producing new tools in the industrial revolution. Advocates of nanotechnology expect a similar surge as tools become microscopic in size.

Functions

One can classify tools according to their basic functions:

• Cutting tools, such as the knife, scythe or sickle, are wedge-shaped implements that produce a shearing force along a narrow face. Ideally, the edge of the tool needs to be harder than the material being cut or else the blade will become dulled with repeated use. But even resilient tools will require periodic sharpening, which is the process of removing deformation wear from the edge. Other examples of cutting tools include gouges and drill bits.
• Moving tools move large and tiny items. Most are levers which give the user a mechanical advantage. For example, concentrating-force tools: the hammer moves a nail, the maul moves a stake, or a whip moves flesh on a horse. These operate by applying physical compression to a surface. In the case of the screwdriver, the force is rotational and called torque. Writing implements deliver a fluid to a surface via compression to activate the ink cartridge. Also grabbing and twisting nuts and bolts with pliers, a glove, a wrench, etc. All these tools move items by some kind of force. Also trucks, rockets and airplanes move larger items and particle accelerators move very small items.
• Tools that enact chemical changes, including temperature and ignition, such as lighters and blowtorches.
• Guiding, measuring and perception tools include the ruler, glasses, set square, sensors, straightedge, theodolite, microscope, monitor, clock,phone, printer
• Shaping tools, such as molds, jigs, trowels.
• Fastening tools, such as welders, rivet guns, nail guns, or glue guns.
• Information and data manipulation tools, such as computers, middleware, IDE, spreadsheets

Some tools may be combinations of other tools. An alarm-clock is for example a combination of a measuring tool (the clock) and a perception tool (the alarm). This enables the alarm-clock to be a tool that falls outside of all the categories mentioned above.

There is some debate on whether to consider protective gear items as tools, because they do not directly help perform work, just protect the worker like ordinary clothing. They do meet the general definition of tools and in many cases are necessary for the completion of the work. Personal protective equipment includes such items as gloves, safety glasses, ear defenders and biohazard suits.

Tool substitution

Often, by design or coincidence, a tool may share key functional attributes with one or more other tools. In this case, some tools can substitute for other tools, either as a makeshift solution or as a matter of practical efficiency. "One tool does it all" is a motto of some importance for workers who cannot practically carry every specialized tool to the location of every work task; such as a carpenter who does not necessarily work in a shop all day and needs to do jobs in a customer's house. Tool substitution may be divided broadly into two classes: substitution "by-design", or "multi-purpose" use, and substitution as makeshift. Substitution "by-design" would be tools that are designed specifically to accomplish multiple tasks using only that one tool. Substitution as makeshift is when human ingenuity comes into play and a tool is used for its unintended purpose such as a mechanic using a long screw driver to separate a cars control arm from a ball joint instead of using a tuning fork. In many cases, the designed secondary functions of tools are not widely known. As an example of the former, many wood-cutting hand saws integrate a carpenter's square by incorporating a specially shaped handle that allows 90° and 45° angles to be marked by aligning the appropriate part of the handle with an edge and scribing along the back edge of the saw. The latter is illustrated by the saying "All tools can be used as hammers." Nearly all tools can be used to function as a hammer, even though very few tools are intentionally designed for it and even fewer work as well as the original.

Tools are also often used to substitute for many mechanical apparatuses, especially in older mechanical devices. In many cases a cheap tool could be used to occupy the place of a missing mechanical part. A window roller in a car could easily be replaced with a pair of vise-grips or regular pliers. A transmission shifter or ignition switch would be able to be replaced with a screw-driver. Again, these would be considered tools that are being used for their unintended purposes, substitution as makeshift. Tools such as a Dremel would be considered the substitution "by-design", or "multi-purpose". This class of tools allows the use of one tool that has at least two different capabilities. "Multi-purpose" tools are basically multiple tools in one device/tool. Tools such as this are often power tools that come with many different attachments like a Dremel does, so you could say that a power drill is a "multi-purpose" tool because you can do more than just one thing with a power drill.

Multi-use tools

Bicycle multi-tool

A Multi-tool is a hand tool that incorporates several tools into a single, portable device; the Swiss army knife represents one of the earliest examples. Other tools have a primary purpose but also incorporate other functionality - for example, lineman's pliers incorporate a gripper and cutter, and are often used as a hammer; and some hand saws incorporate a carpenter's square in the right-angle between the blade's dull edge and the saw's handle. This would also be the category in which the "multi-purpose" tools since they are also multiple tools in one (multi-use and multi-purpose can be used interchangeably). These types of tools were specifically made to catch the eye of many different craftsman who traveled to do their work. To these workers these types of tools were revolutionary because they were one tool or one device that could do several different things. With this new revolution of tools the traveling craftsman would not have to carry so many tools with them to job sites, being that their space would be limited to the vehicle they were driving. The problem of having to deal with so many different tools was solved with the overtaking of multi-use tools.

Use by animals

A Bonobo at the San Diego Zoo "fishing" fortermites

Observation has confirmed that a number of species can use tools including monkeys, apes, elephants, several birds, and sea otters. Philosophers originally thought that only humans had the ability to make tools, until zoologists observed birds and monkeys making tools. Now the unique relationship of humans with tools is considered to be that we are the only species that uses tools to make other tools.

Tool metaphors                                          telephone is a communication tool that interfaces between two people engaged in conversation at one level. It also interfaces between each user and the communication network at another level. It is in the domain of media and communications technology that a counter-intuitive aspect of our relationships with our tools first began to gain popular recognition. Marshall McLuhan famously said "We shape our tools. And then our tools shape us." McLuhan was referring to the fact that our social practices co-evolve with our use of new tools and the refinements we make to existing tools.

In North American colloquialism, the word "tool" may be loosely used to describe an individual of low mental capacity (essentially, an "idiot") or someone who fails to realise that they are being taken advantage of by others.This metaphor is drawn from the understanding that tools (as understood by most of society) are objects that are used for specific tasks.

Eliminating slug pulling during piercing operations

Slug pulling is the tendency for a pierced-out slug to stick to the face of the pierce punch during withdrawal. If the slug pulls out of the matrix (button) and falls off the punch face, it may cause double metal to be introduced into the die, resulting in die shearing, broken punches, broken die steel, surface defects, and numerous other problems.

It's truly amazing (or amusing) just how many dies are designed and built with very little attention given to the problem of slug pulling. In an effort to reduce die cost, stampers often procure the cheapest possible punches and buttons, including punches without slug ejectors.

Slug pulling often can be a big problem with progressive dies, but it also can be a problem with larger single-station or transfer dies.

Slug pulling is caused by several factors:

• A small vacuum pocket is created during piercing between the face of the pierce punch and slug.
• Lubricants cause a "gluing" effect.
• Cutting clearance is excessive.
• Suction is created between the punch and matrix during punch withdrawal.

Figure 1 Pierce punches equipped with slug ejector spring pins are commercially available from most pierce punch providers.	Figure 2 The urethane must be ground flat on three sides to allow for expansion on sheet metal contact and then press-fit into the punch end.

How the stamper uses two basic items involved in piercing—the punch and the matrix—can help decrease or eliminate slug pulling. Of course, these solutions will not work for every application.

The Pierce Punch

Spring-loaded Slug Ejector Pins. Pierce punches equipped with slug ejector spring pins are commercially available from most pierce punch providers (see Figure 1). Most punches have some type of provision for locking the pin in its full depressed position. This allows for the punch to be sharpened while maintaining the same spring travel.

The small hole in the side of the punch allows for a spring retention pin to be inserted. It also should allow trapped air to travel around the pin and out the hole. Often the spring pin fits like a piston in the hole and does not allow for trapped suction to be relieved. An ideal spring ejector has a somewhat sloppy pin.

These types of ejectors work well in slower single-station operation but often fail in high-speed progressive dies.

Punches purchased without slug ejector pins can be jury-rigged later if time and financial resources are limited. This quick fix consists of a small piece of urethane inserted into the end of a punch that has had a hole burned or carbide drilled into its tip. The urethane must be ground flat on three sides to allow for expansion on sheet metal contact and then press-fit into the punch end (see Figure 2).

Figure 3 During piercing, the slug that's created has a natural curvature. It causes a vacuum pocket, which makes the slug stick to the face of the punch, resulting in slug pulling.	Figure 4 Rooftop shear, cone-shaped punch tip, and balled punch face all force the slug to deform into a longer length of line before most of the cutting takes place.

Slotted Punch Face. During piercing, the slug that's created has a natural curvature. It causes a vacuum pocket, which makes the slug stick to the face of the punch, resulting in slug pulling (see Figure 3). Slotting or grinding grooves in the punch face helps relieve the suction created between the face of the punch and the slug.

Rooftop Shear, Cone-shaped Punch Tip, and Balled Punch Face. All three of these methods force the slug to deform into a longer length of line before most of the cutting takes place. This allows the slug to expand in the matrix and resist pulling up with the punch (see Figure 4).

Air Blown Through the Punch. A timed blast of air through the pierce punch can remove the slug from the punch face. However, a continuous flow of air through the punch could cause vital lubricant to be blown away during the piercing process.

The Matrix

Slug-retention Matrix. A slug-retention button (see Figure 5) consists of two small slots machined at an angle in each side of the matrix. These slots cause a burr to be generated on the slug. The burr is forced downward at an angle, wedging the slug in the matrix.

With a slug-hugger button (see Figure 6), barbs in the matrix impale themselves into the slug. An industrial quick-fix alternative to the slug hugger is to place tiny weld spatter on the inside of the pierce hole.

Reverse-tapered Matrix. This method may look a little strange at first, but if the matrix is properly manufactured, it works pretty well.

Figure 5 A slug-retention button consists of two small slots machined at an angle in each side of the matrix. These slots cause a small burr to be generated on the slug.	Figure 6 With a slug-hugger button, barbs in the matrix impale themselves into the slug.	Figure 7 A reverse-tapered button allows for the slug to be held in compression in the matrix.

Most die buttons have a bell mouth taper machined into them, with the hole diameter increasing toward the bottom of the button. A reverse-tapered button gets smaller in diameter to a certain point and then increases in diameter. This reverse taper allows for the slug to be held in compression in the matrix (see Figure 7).

Vacuum Slug Removal. Vacuum units are available to pull slugs from the punch face. While these work well, they can be expensive.

Slug pulling is a serious and costly problem in cutting and piercing operations and should not be taken lightly. There are many more methods to prevent it than those discussed here, and spending a little extra time and a little money addressing this problem will save stampers even more in the end. 

Discusses the fundamentals of drawing and stretching

What Is Drawing?

 

Figure 1

Drawing is a metal forming process in which a product is made by controlling sheet metal flow into a cavity and over a punch. The process of deep drawing means that the part must be taller than its minimum width.

Many people confuse drawing with stretching. True drawing results in very little stretching of the metal. Drawing requires metal flow, while stretching does not. It is only through the drawing process that objects such as oil pans, beer kegs, and oil filters can be made.

Drawing can be better defined as the process of displacing pre-existing surface into an alternate-shaped vessel containing nearly the same surface area. Stretching can be defined as the increase of surface area that results in a product with more surface area than the original surface area.

Drawing requires the metal to feed inward toward the punch. Very little or no metal flow takes place during stretching. However, keep in mind that because drawing does require tension to pull the metal inward, some stretching occurs during drawing.

The key in deep drawing is to limit the amount of metal stretching and thinning that take place. Items such as oil pans require significant drawing and stretching. Achieving a deep-drawn product that exhibits very little metal thinning requires extensive knowledge of sheet metal properties, drawing ratios, radii, and friction.Figure 1 shows the drawing process.

Basic Drawing Components

 

Figure 2

the deep-drawing process is not directional-specific. in other words, the direction in which the drawing takes place really doesn't matter. you can draw a part up or down into a cavity. you can even draw a part vertically using cams or special vertical-motion presses.

please keep in mind that i am in no way indicating that process engineers or die designers don't pay close attention to the direction in which are drawing. drawing direction must be given careful attention because it affects the ability to move, cut, and eject the part in the die. if drawing is incorporated into a progressive die, the drawing direction also may affect the die and strip carrier design.

Figure 2 shows a section view of a very simple single-action drawing die. this die is designed to produce a round cup with a small flange. a basic drawing die consists of the following components:

1. Die set or foundation. This could be made of mild steel cast iron or aluminum. It serves as the guided foundation on which all of the metal forming sections will be mounted.

2. Draw cavity. The draw cavity represents the drawing die's female portion. Uually made from tool steel or solid carbide, it serves as the cavity in which the metal is formed.

3. Ejectors and knockouts. These pressure-loaded components serve to push or eject the part from the draw cavity. a high-pressure knockout must be timed properly so that it pushes the part out of the cavity after the die has fully separated. If the knockout is timed incorrectly, the part can be crushed during the return stroke of the press.

An alternate method to using a knockout is to use a small ejector pin and a lightweight spring. this spring must have enough force to eject the part adequately but not deform it during the press's return stroke. The pin and spring method does not require specific timing. However, keep in mind that certain part geometries require a great deal of force to eject from the cavity. in such cases, a timed high-pressure knockout may be necessary.

4. Air vents. Air can be trapped during drawing. This trapped air must be vented out of the tool. Not venting the air can cause defective parts, splitting, and wrinkling, as well as make it difficult to strip the drawn part from the cavity.

It is critical that both the cavity and punch contain air vents. Air vents in the cavity allow trapped air to escape during the downstroke of the press; air vents in the punch allow air to be pulled into the punch, which prevents suction during the part-stripping process.

5. Die face. The die face is the surface surrounding the cavity. it can be a flat or a contoured surface. this surface interfaces with the sheet metal and keeps it from wrinkling during the drawing process. the die face typically is made of tool steel or carbide and is highly polished in the direction of metal flow.

6. Draw punch. This component represents the male shape of the drawn part geometry. Like the cavity, it usually is made of tool steel. In most cases, it is polished to a mirrorlike surface. However, there are times when a rough surface is desired.

 

Figure 3

7. Blank holder /draw pad / binder. This pressure-loaded plate, which serves to keep the metal from wrinkling during the drawing process, typically is loaded with gas springs. However, certain drawing dies can achieve the force needed to control metal flow through the use of a press cushion.

8. Pressure system. The pressure system supplies the force necessary to control metal flow. It may consist of gas, coil, hydraulic, or urethane springs. Certain drawing dies utilize a press cushion to obtain the needed pressure. A press cushion is a plate or series of vertically moving thick, flat plates mounted beneath the press's bolster plate. These plates transfer the force to the bottom of the draw pad using a cushion pin (Figure 3).

9. Equalizer block. This block functions to maintain a specific gap between the die face and the draw pad surface. It also allows for minor adjustments to be made with respect to how much pressure is being applied to the blank.

Defines slug pulling and common causes

Slug pulling is a serious problem in a stamping operation. Addressing the issue requires first understanding why the slugs are pulling.

What Is Slug Pulling?

When a pierce punch creates a hole, it also produces scrap, usually referred to as a slug. Slug pulling occurs when the slug sticks to the punch face upon withdrawal and comes out of the button, or lower matrix.

If a slug falls off the punch and onto the strip or part, it can damage the part and die. Keeping the slug down in the matrix or, better yet, completely pushing it out of the die is the desired scenario.

What Causes Slug Pulling?

Many factors contribute to slug pulling. Among them are trapped air; large cutting clearances; extremely fast piercing operations; sticky lubricants; improperly demagnetized punches; and fatigued or insufficient spring ejectors.

1. Trapped air/ vacuum pockets. The slug generated during the piercing process has some curvature. The curved, void areas where air is trapped, creating a vacuum action. During the perforating process, a tight seal is maintained around the punch perimeter. When the punch is withdrawn, this seal prevents the slug from coming off the punch (Figure 1a). Keep in mind that the only portion of the piercing punch that makes contact with the metal is a localized zone around the punch's outside diameter. Even punches with angularity make only localized contact with the metal (Figure 1b).

Trapped air must be allowed to escape to reduce the amount of vacuum. This is done by creating a small air vent in the center of the pierce punch, which allows the otherwise trapped air to exhaust itself from the vent hole and reduce the suction. Losing suction breaks the seal between the slug and the pierce punch and allows the slug to fall (Figure 2a).

When piercing punches that are too small to vent are used, other means of addressing slug pulling most likely will be necessary. Also keep in mind that addressing the trapped air probably won't solve the slug pulling issue completely, but it will certainly help.

2. Larger cutting clearances. Although using engineered or larger cutting clearances can result in much greater punch and matrix life, there is one drawback to doing so. As the clearance gets larger, compression on the slug decreases, which increases the chances of slug pulling.

When smaller cutting clearances are used during the perforating process, both the slug and metal outside the slug are forced into compression. After the slug is cut free, it decompresses and remains in the matrix. This is because the decompressed slug now has an interference or press fit into the matrix.

In simple terms, when greater cutting clearances are used, the slug will be slightly smaller than the hole in the matrix, which means it may be pulled from the matrix by the punch, resulting in slug pulling. Reducing the cutting clearance certainly can help this problem, but it also can shorten punch life and increase sharpening frequency. Rather than reducing the cutting clearance, it is recommended stampers try a few methods that will be discussed in the next part of this series (Figure 2b).

3. Oil / lubricant problems. Using heavy, thick, highly viscous oils and deep-drawing lubricants only adds to slug pulling problems. Unfortunately, these compounds often are necessary for forming dies to perform correctly.

Over time heavy oils and compounds can become coagulated and sticky. Thick, sticky compounds can cause slugs to stick to punches. Periodically cleaning the cutting components can help to resolve this sticky residue problem. 

4. Magnetized punches. Punches and die sections often are sharpened with a surface grinder. Most surface grinders secure the sections and punches to be ground by a high-power electro- or conventional magnet. Any ferrous metal that comes in contact with this magnet becomes slightly magnetized.

After the die components have been ground, they then must be demagnetized fully. This process is accomplished by using a commercially available demagnetizing unit. Magnetized pierce punches and die sections can cause slugs and other magnetic debris to be picked up and carried through the tool.

5. Weak or fatigued spring ejectors. Spring ejectors often are used in piercing and cutting punches. These small, spring-loaded pins push the slug from the punch face after cutting has taken place. If the spring behind the punch fails or fatigues, slug pulling can occur. Periodically inspecting and replacing springs is a necessary part of a good die maintenance program (Figure 4).

 

Figure 4

Spring Ejectors

Slug pulling can have disastrous consequences. A single slug carried through a progressive die can damage every tool in the station. The next part in this series will discuss methods for resolving slug pulling problems.