Tooling and Toolmaking Process Handbook: Manufacturing Processes

Manufacturing Processes

A single misaligned die clearance cost a factory 40,000 rejected parts in one shift. Here's everything you need to know so it never happens to you.

the practitioner stared at the pile of blanked steel parts on the inspection table and felt his stomach drop. Every single one had ragged, torn edges — the kind of defect that screams "wrong clearance" to anyone who has spent time in a press shop. His company had just landed their biggest contract, and the first production run was scrap.

The problem wasn't the press. It wasn't the material. It was the tooling.

Tooling and toolmaking sit at the invisible center of every manufactured product you have ever touched. The phone in your pocket, the car you drive, the appliance in your kitchen — every one of them passed through a punch, a die, a mold, or a laser-cut profile at some point in its creation. Yet tooling remains one of the most misunderstood and undervalued disciplines in manufacturing.

This guide changes that. Whether you are a beginner learning the fundamentals, an experienced machinist looking for reference data, or a decision-maker evaluating manufacturing methods, what follows is a complete, reference-grade guide to tooling and toolmaking — from punches and dies to EDM, from steel rule dies to laser processing, from sheet metal bending to powder metallurgy tooling.

Bookmark this. Print it. Keep it on your shop floor.

The Foundations: Punches, Dies, and Press Work

Why Clearance Is the Single Most Important Variable in Your Die

the practitioner's problem — and the problem that plagues shops worldwide — comes down to one word: clearance.

The clearance between a punch and die for blanking and perforating is governed by the thickness and kind of stock being operated on. For thin material, the punch should be a close sliding fit to prevent ragged edges. For heavier stock, there must be some clearance. Getting this right reduces the pressure required for the punching operation and prevents broken punches.

But here is where confusion begins.

There is an industry-wide disagreement about what "clearance" even means.

A survey of fifteen firms specializing in die work revealed the following split:

The per-side definition is the prevailing standard, and for good reason. When you work with dies of irregular form or angular shape, defining clearance as the space on each side eliminates the confusion that total-difference definitions create on unsymmetrical forms.

Critical Terminology:

• Cutting clearance = the space between punch and die on each side
• Die clearance = the angular clearance below the cutting edge so parts fall freely through the die

Throughout this guide, "clearance" means the space on one side only. For round dies: clearance = die radius − punch radius.

Clearances You Should Actually Use

Here are the clearance multipliers proven across decades of production:

Where to Apply the Clearance

This trips up even experienced toolmakers. The rule is simple but absolute:

• Blanking to a given size? → The die is made to the required size. The punch is made smaller (clearance is deducted from the punch).
• Perforating holes of a given size? → The punch is made to the required diameter. The die is made larger (clearance is added to the die).

Remember: For blanking, subtract from the punch. For perforating, add to the die.

How Clearance Affects Working Pressure

Clearance does not just affect edge quality — it directly impacts the force your press must deliver.

Real test data demonstrates this relationship clearly:

A counterintuitive fact: soft, ductile metal requires more clearance than hard metal, even though common practice has traditionally been to increase clearance for harder metals. In punching fairly hard steel, clean fractures were obtained with clearance of only 0.03 times stock thickness.

Angular Clearance for Dies

Below the cutting edge, dies need angular clearance so blanked parts fall freely:

There are two methods of giving this clearance:

1. Clearance extends to the top face of the die — Used for very soft metal (soft, thin brass)
2. Straight section (~⅛ inch) below the cutting edge, then clearance below — Used for harder materials (hard brass, steel). This method allows thousands of blanks to be cut with little variation in size, because grinding the die face does not enlarge the hole appreciably.

Lubricants for Press Work: The Invisible Performance Multiplier

the practitioner learned this the hard way on his second production run. Even with perfect clearance, his parts were showing accelerated die wear. The fix was not a new die — it was the right lubricant.

Here is the complete lubrication guide for press work:

Blanking Operations

Key specification: Lubricant thickness needs to be approximately 0.0001 inch, achievable with about 1 pint of fluid to cover 500 square feet of material.

Application methods: Rollers or spray application to the sheet or strip. High-speed blanking may require heavier applications or continuous airless spraying of oil.

Drawing Operations

Deep drawing often involves ironing or thinning of the walls by up to 35 per cent. At these extreme reductions, the additive chemistry maintaining a physical barrier between tool surfaces and the workpiece becomes critical.

Press Speeds, Pressures, and the Formulas You Need

Press Speeds

The Punching Pressure Formula

For a circular hole in sheet steel:

$$F = \frac{\pi \times D \times S \times T}{2000}$$

Where:

• $F$ = force in tons
• $D$ = hole diameter (inches)
• $S$ = shearing strength (lb/in²)
• $T$ = stock thickness (inches)

The Shortcut Formula:

$$F = D \times T \times 80$$

Where $D$ and $T$ are in inches and 80 is the factor for steel. Result is in tons.

Example: Punching a 2-inch diameter hole through ¼-inch steel:

$$F = 2 \times 0.25 \times 80 = 40 \text{ tons}$$

For non-circular holes: Replace the hole diameter with one-third of the perimeter of the hole to be punched.

Example: Punching a 1-inch square hole in ¼-inch steel:

• Perimeter = 4 inches
• One-third of perimeter = 1⅓ inches

$$F = 1.333 \times 0.25 \times 80 = 26.67 \text{ tons}$$

Material-Specific Factors

Example with brass: Punching a 1 × 2 inch hole in ¼-inch brass:

• Perimeter = 6 inches
• Factor = 6 ÷ 3 = 2

$$F = 2 \times 0.25 \times 65 = 32.5 \text{ tons}$$

Shut Height of Press

The shut height is the die space when the slide is at the bottom of its stroke and the slide connection has been adjusted upward as far as possible. Two definitions exist:

1. Distance from the lower face of the slide to the top of the bed
2. Distance from the lower face of the slide to the top of the bolster plate

The safest practice is to define shut height as the distance from the top of the bolster to the bottom of the slide, with the stroke down and the adjustment up. A misunderstanding that results in too much die space is far less serious than having insufficient die space.

Drawing Cylindrical Shells: Blank Diameters and Reduction Limits

This is where the practitioner's shop transitioned from blanking to forming — and where the math becomes essential.

Calculating Blank Diameters

For sharp-cornered shells (thin stock):

$$D = \sqrt{d^2 + 4dh}$$

Where:

• $D$ = diameter of flat blank
• $d$ = diameter of finished shell
• $h$ = height of finished shell

Example: Shell diameter = 1.5 inches, height = 2 inches:

$$D = \sqrt{1.5^2 + 4 \times 1.5 \times 2} = \sqrt{2.25 + 12} = \sqrt{14.25} = 3.78 \text{ inches}$$

For round-cornered cups (where $r$ = radius of corner, not exceeding ¼ the height):

$$D = \sqrt{d^2 + 4dh} - r$$

When thickness reduction occurs during drawing, calculate the "mean height" first:

$$M = \frac{h \times t}{T}$$

Where:

• $M$ = approximate mean height of drawn shell
• $h$ = height of drawn shell
• $t$ = thickness of shell after drawing
• $T$ = thickness of metal before drawing

Then use $M$ in place of $h$ in the blank diameter formula.

Example: Shell 2 inches diameter, 3¾ inches high, original stock = 0.050 inch, drawn shell = 0.040 inch:

$$M = \frac{3.75 \times 0.040}{0.050} = 3.0 \text{ inches}$$

The blank diameter for a 2-inch shell at 3-inch height = 5.29 inches (from standard reference tables).

Note: This formula is accurate unless the reduction in thickness exceeds about one-fifth the original thickness. When there is considerable reduction, the blank will produce a shell that is slightly too long — but the error is in the right direction, since drawn shell edges are ordinarily trimmed.

Depth and Diameter Reduction Limits

The depth to which metal can be drawn in one operation depends on material quality, thickness, die angle, and the amount of ironing.

The fundamental rule: The depth or length of the first draw should never be greater than the diameter of the shell.

Alternative rule: The depth of the first draw should equal one-third the diameter of the blank.

Practical guideline: Sheet steel of any thickness up to ¼ inch can typically be drawn so that the shell diameter equals about six-tenths of the blank diameter on the first draw.

Successive Reduction Limits (Single-Action Presses)

These figures assume annealing after the first draw, and at least between every two following operations:

For double-action presses (where the inside of the cup is supported by a bushing during drawing), reductions can be increased to 30%, 24%, 18%, 15%, and 12% respectively. These higher figures also apply to brass in single-action presses.

On ironing: The extent to which a shell can be ironed in one drawing operation ranges between 0.002 and 0.004 inch per side, and should not exceed 0.001 inch on the final draw if a good finish is required.

Annealing Drawn Shells

When drawing steel, iron, brass, or copper, annealing is necessary after two or three draws because the metal work-hardens during drawing.

• Steel and brass: Anneal between alternate reductions, at minimum
• Tin plate or finished stock: Must ordinarily be drawn to size in one or two operations (annealing would ruin the finish)
• Aluminum: Can be drawn deeper with less annealing than other commercial metals. If annealing is necessary, heat in a muffle furnace — temperature must not exceed 700°F
• Brass: By heating to just below a dull red (visible in a dark room), you can draw difficult shapes that are otherwise almost impossible, and produce shapes with square corners

Drawing Rectangular Shapes

The radius of the corners should be as large as possible — defects occur in the corners during drawing, and smaller radii reduce achievable depth.

These figures are from actual production and can be slightly exceeded with metals prepared specifically for drawing.

Bending Sheet Metal: Formulas That Actually Work

Every bent part starts with a question: How long should the straight stock be before bending?

The answer depends on the material, the bend radius, the bend angle, and the tooling. Here are the proven formulas from extensive experiments at an electrical manufacturer, applicable to parts bent with simple tools or on the bench, with limits of ± 1/64 inch.

Degree Bend Formulas

For soft brass and soft copper:

$$L = (0.55 \times T) + (1.57 \times R)$$

For half-hard copper, brass, soft steel, and aluminum:

$$L = (0.64 \times T) + (1.57 \times R)$$

For bronze, hard copper, cold-rolled steel, and spring steel:

$$L = (0.71 \times T) + (1.57 \times R)$$

Where:

• $L$ = length of straight stock required for the bend (inches)
• $T$ = thickness (inches)
• $R$ = inside radius of bend (inches)

Bends at Angles Other Than 90 Degrees

For any angle: Calculate $L$ using the formulas above, then multiply by:

$$L_{actual} = L \times \frac{\text{Angle of Bend}}{90}$$

Critical distinction: The "angle of bend" is the angle through which the material has actually been bent — not necessarily the angle shown on the drawing.

• A drawing showing 60° may mean the bend angle is 120° (180° − 60° = 120°)
• A drawing showing the bend explicitly as 60° means the bend angle is 60°
• A 30° offset from 90° means the bend angle is 60° (90° − 30° = 60°)

Worked Example: Multiple Bends in Soft Steel

A part has:

• A 180° bend at one end (R = 3/8 inch, T = 1/8 inch)
• A 60° bend at the other end (R = 5/8 inch, T = 1/8 inch)
• A 3.5-inch straight section between bends

For the 180° bend (soft steel):

$$L = [(0.64 \times 0.125) + (1.57 \times 0.375)] \times \frac{180}{90} = 1.338 \text{ inches}$$

For the 60° bend (soft steel):

$$L = [(0.64 \times 0.125) + (1.57 \times 0.625)] \times \frac{60}{90} = 0.707 \text{ inches}$$

Total length before bending: 3.5 + 1.338 + 0.707 = 5.545 inches

Alternative Bending Allowance Method

For general sheet metal work (counters, bank fittings, office fixtures) where extreme precision is not required:

Add ⅓ to ½ of the stock thickness for each bend to the sum of the inside dimensions of the finished piece. Use ⅓ for soft stock and ½ for hard material.

For V-die (semi-square) bends:

$$X = 1.67 \times B \times G$$

Where:

• $X$ = amount to deduct from sum of outside bend dimensions
• $B$ = number of bends
• $G$ = decimal equivalent of the gage

For drawn or rolled (square) bends:

$$X = 1.33 \times B \times G$$

Bend Deduction Reference Table (V-Die Bends)

Bend Deduction Reference Table (Drawn/Rolled Square Bends)

Fine Blanking: When Standard Stamping Is Not Enough

Six months into his contract, the practitioner needed parts with edges so clean they required no secondary machining. Conventional stamping could not deliver. His engineering team recommended fine blanking — and it transformed the product line.

What Makes Fine Blanking Different

Fine blanking uses special presses and tooling to produce flat components from sheet metal or plate with high dimensional accuracy. The process was pioneered by Hydrel A.G. of Romanshorn, Switzerland, and requires three separate and distinct press movements:

1. Clamping the work material
2. Performing the blanking operation
3. Ejecting the finished part

Forces of 1.5 to 2.5 times those used in conventional stamping are needed, so machines and tools must be designed and constructed accordingly.

Press Types for Fine Blanking

Tooling Materials

The Critical Role of V-Projections

V-projections are the secret behind fine blanking's extraordinary edge quality. These are sharp projections of 90° V-section that follow the outline of the workpiece, incorporated into the stripper plate (and into the die plate for thicker material).

How they work:

1. Pressure is applied before the blanking operation begins
2. The sharp V-edges bite into the material surface near the contour edges
3. This prevents sideways movement of the blank
4. The pressure squeezes material toward the cutting edges, reducing the rounding effect normally seen at cut edges
5. For small details (like gear teeth), V-projections are used on both sides of the work to enhance the flow effect

Cutting clearances between the intermediate punch and die are held between 0.0001 and 0.0003 inch — drastically tighter than conventional stamping.

Fine Blanking Performance Specifications

Calculating Fine Blanking Forces

Cutting force (lb):

$$F_{cut} = 0.9 \times L_c \times T \times \sigma_t$$

Where:

• $L_c$ = length of cut (inches)
• $T$ = material thickness (inches)
• $\sigma_t$ = tensile strength (lbf/in²)

Clamping force (V-projection pressure):

$$F_{clamp} = L_v \times h \times \sigma_t \times f$$

Where:

• $L_v$ = length of V-projection (inches)
• $h$ = V-projection height (inches)
• $\sigma_t$ = tensile strength (lbf/in²)
• $f$ = empirical factor (2.4 to 4.4 for tensile strengths of 28,000–113,000 lbf/in²)

Rule of thumb: Clamping pressure is approximately 30% of the cutting force.

Design Considerations for Fine Blanking

• Strip width must be 2–3 times the material thickness, plus the width of the part measured transverse to the feed direction
• Additional operations such as countersinking, coining, and bending up to 60° can be incorporated into fine-blanking tooling
• Distortion may occur with thin materials due to release of internal stresses
• V-projection placement affects tool life — too close to the cut, and the projection may move out of the material at the start of cutting; too far, and material waste and blanking force increase

Steel Rule Dies: The Versatile Toolmaking Solution

When the practitioner needed to prototype a new product line with complex contours but could not justify the cost of conventional hardened dies, his veteran toolmaker suggested steel rule dies. It was a revelation.

What Are Steel Rule Dies?

Steel rule dies use strips of hardened steel (the "rules") held on edge in slots cut into a die block, with the sharp cutting edge facing the workpiece. They are versatile, relatively fast to make, and cost-effective for many applications.

Die Block Materials

Lignostone is made from approximately 35 plies of highly compressed lignite wood, bonded with phenolformaldehyde resin, providing great density and strength.

Making Steel Rule Dies: The Process

Step 1: Slot Cutting

• Narrow slots are cut with a jig saw to hold steel strips vertically
• The saw blade must always be maintained vertical to the board
• Magnifying lenses are often used to keep the blade close to the line
• Carbide or carbide-tipped saw blades are recommended for clean cuts and long life
• Trial cuts on scrap die block ensure the rule thickness will be a tight fit

Step 2: Creating Bridges

• "Islands" (like the center of a circle) are kept in position by cutting some portions of the slot to less than full depth
• Bridge lengths: ¼ to ½ inch
• Bridge heights: ⅝ to ¾ inch
• Matching slots must be cut in the steel rules on the non-cutting side to accommodate these bridges

Step 3: Bending the Rules

• Rules are bent using small, purpose-built bending machines
• For small radii (jig saw puzzles, etc.), the tooling performs a peening or hammering action
• Complex forms are made in two or more pieces, joined by welding or brazing
• Edges to be joined are mitered for a perfect fit and clamped securely
• Electrical resistance or gas torch is used for heating; wet rags are applied adjacent to the joint to prevent heat damage to the preset hardness

Cutting Edge Profiles

Steel rule cutting edges come in several profiles:

Heat Treatment of Steel Rules

For the dead-soft material, the heat treatment cycle consists of:

1. Carburizing in liquid compound at 1500°F
2. Quenching in oil
3. "Tough" tempering at 550°F
4. Cooling in the furnace

Piercing Punches in Steel Rule Dies

Punches incorporated into steel rule dies for piercing holes, cutting slots, or forming ribs are preferably made from high-carbon, high-vanadium alloy steel:

Final Assembly and Clearance Setting

After the hardened rule is reinstalled in the die block:

1. The tool is loaded into the press
2. The sharp die is used carefully to shear the pad sides to match die contours exactly
3. Clearances are set at about half those used in conventional blanking dies
4. Adjustments are made by grinding the die steel or the punch
5. Sharp edges are ground flat to produce a land of about 1/64 inch wide for the working die edges

Electrical Discharge Machining (EDM): The Toolmaker's Secret Weapon

If punches, dies, and steel rule dies represent the foundations of toolmaking, EDM represents its future. When the practitioner needed to create complex mold cavities in hardened tool steel — shapes that no conventional cutter could reach — his shop invested in EDM capability. It changed everything.

What Is EDM?

Electrical Discharge Machining uses an electrode to remove metal from a workpiece by generating electric sparks between conducting surfaces. The process works on any conductive material regardless of hardness, making it invaluable for working hardened tool steels, carbides, and exotic alloys.

The Two Main Types of EDM

EDG (Electrical Discharge Grinding) is a specialized variant using a graphite wheel electrode up to 12 inches in diameter, mainly for producing complex profiles on polycrystalline diamond cutting tools and for shaping carbide tooling.

How the EDM Process Works

The sparking cycle is remarkably precise:

1. Current starts flowing between the electrode and the workpiece
2. Dielectric fluid in the smallest gap area transforms into a plasma of hydrogen, carbon, and various oxides
3. This plasma forms a conducting passageway of ionized particles
4. A spark forms between electrode and workpiece, heating and vaporizing a tiny area
5. The striking voltage is reached, voltage drops, and the ionized field loses energy
6. The spark can no longer be sustained — the electrical supply is cut off by the control
7. The plasma implodes, creating a low-pressure pulse that draws in dielectric fluid
8. Dielectric fluid flushes away debris and cools the impinged area
9. The cycle repeats (typically lasting a few microseconds)

Essential EDM Terminology

Dielectric Fluids

Critical safety note: Gases generated by sparking may explode if trapped, causing danger to life, breaking electrodes or workpieces, or causing fire. Flushing systems must prevent gas entrapment.