Manufacturing Process Selection from Raw Material to Finished Part: Fine Blanking

Fine Blanking — When Standard Stamping Isn't Precise Enough

Fine blanking uses special presses and tooling to produce flat components with high dimensional accuracy. It requires forces 1.5 to 2.5 times those of conventional stamping.

Three distinct press movements required:

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

Cutting clearances in fine blanking:

V-Projections — The Secret to Fine Blanking Quality:

Sharp V-shaped projections follow the outline of the workpiece on the stripper plate (and on the die plate for material > 0.15 inch). These projections bite into the material surface before blanking begins, preventing sideways movement and squeezing material toward the cutting edges — reducing the rounding effect at the cut edge.

V-Projection Dimensions (Stripper Plate Only):

V-Projections on Both Stripper and Die Plate:

Tooling materials for fine blanking:

• Cutting elements: 12% chromium steel (standard); high-speed steel or tungsten carbide for long runs
• Mechanical presses: Toggle-type, limited to ~280 tons total force
• Higher forces: All-hydraulic designs required

Steel Rule Dies — Cost-Effective Blanking

Patented by the practitioner in 1879, steel rule dies (knife dies) use cutting edges made from steel strips of the same proportions as graduated measuring rules. They typically cost 25 to 35 percent of conventional blanking dies and can be produced in much less time.

Die block materials:

Steel rule specifications:

Heat treatment for steel rules:

Piercing punches in steel rule dies: Made from high-carbon, high-vanadium alloy steel, heat treated to Rc 61–63 with head ends tempered to Rc 45–50.

Electrical Discharge Machining (EDM) — When Cutting Isn't Cutting

Six months into his deep dive, the practitioner faced a challenge no conventional process could solve: machining hardened tool steel die cavities to tolerances measured in ten-thousandths of an inch. That's when he discovered EDM.

How EDM Works — The Science of Controlled Sparks

EDM uses an electrode to remove metal from a workpiece by generating electric sparks between conducting surfaces. Unlike cutting, grinding, or milling, EDM doesn't require a tool harder than the workpiece — it removes material through thermal erosion.

The two main types:

The EDM Spark Cycle — What Happens in Microseconds

1. Current flows between electrode and workpiece across the smallest gap
2. Dielectric fluid in that gap transforms into a plasma of hydrogen, carbon, and oxides
3. The plasma creates a conducting passageway of ionized particles
4. A spark forms, heating and vaporizing a tiny area of the workpiece
5. Striking voltage is reached, voltage drops, the ionized field loses energy
6. The spark extinguishes — the plasma implodes
7. This implosion creates a low-pressure pulse that draws in dielectric fluid
8. Fresh fluid flushes away debris and cools the impinged area
9. The cycle repeats — thousands of times per second

A typical cycle lasts just a few microseconds (millionths of a second).

Essential EDM Terminology

Electrode Materials — Choosing the Right One

Graphite dominates EDM electrode production. Here's why:

• Sublimation, not melting: Graphite changes directly from solid to gas at 3,350°C (6,062°F) — it never passes through a liquid state
• Superior metal removal rate compared to copper
• Density: 1.55 – 1.85 g/cm³ (lighter than most metals)
• Wear resistance: Fine-grain, high-density grades resist wear better than coarse grades
• Cost: Premium grades cost up to 5× the least expensive, but savings during machining often justify the cost

Other electrode materials and their characteristics:

Workpiece Material Properties for EDM

Matching rule: The melting points and specific gravities of electrode and workpiece material should preferably be similar.

Workpiece-electrode pairing recommendations:

• Aluminum, brass, copper workpieces → Use metallic electrodes (copper, copper-tungsten) with low melting points
• Carbon and stainless steel workpieces → Use graphite electrodes (high melting points)
• Tungsten carbides → Use copper-tungsten electrodes with high frequencies

EDM Machine Settings and Performance

Power selection rule of thumb: 50 to 65 amps per square inch of electrode engagement.

Example: A 1/2-inch square electrode: 0.5 × 0.5 × 50 = 12.5 amps

Polarity effects:

Effect of Electrical Controls on EDM Operations:

Key insight: Halving the on and off times while keeping the same duty cycle (40%) doubled the frequency but reduced MRR slightly while improving surface finish from 400 to 300 µin. Ra — at the cost of electrode wear jumping from 2.5% to 6.3%.

The Recast Layer — EDM's Hidden Problem

One drawback of EDM on steel is the recast layer. The dielectric oil causes the operation to become a random heat-treatment process: metal is heated to extreme temperatures, then quenched in oil. The oil breaks down into hydrocarbons, and the molten metal traps carbon atoms, forming a very thin, hard, brittle surface called the recast layer over the heat-affected zone (HAZ).

On wire EDM machines with deionized water as the dielectric, carbon is extracted rather than added. When copper wire is used, copper atoms migrate into the recast layer, slightly softening the surface. With proper adjustment, the HAZ depth can be held below 1 micron (0.00004 inch).

Flushing — The Make-or-Break Factor

Flushing is vital to successful EDM. Methods include:

• Pressure flushing: Fluid pumped through holes in the electrode or workpiece
• Vacuum flushing: Used when straight side walls are required
• Side nozzle flushing: Fluid directed from tank surrounding the workpiece

Warning: Excessive flushing pressure can displace the electrode or workpiece, causing inaccuracy. Many low-pressure flushing holes are preferable to a few high-pressure holes. Pressure-relief valves are recommended.

Safety alert: Gases generated by sparking may explode, break electrodes/workpieces, or cause fire if entrapped.

Wire EDM Specifics

Wire specifications:

Wire coatings: Zinc is favored because its low melting temperature (419°C) and vaporization temperature (906°C) allow the coating to boil off while the brass core (melts at 930°C) continues delivering current — resulting in faster cutting and reduced wire breakage.

Drilling holes for wire EDM:

• EDM can drill a 0.04-inch hole through 4-inch thick steel in about 3 minutes using brass or copper tubing
• Practical minimum: 0.012 inch diameter (limited by overcut, tubing rigidity, electrode wear)
• Practical maximum: 0.12 inch diameter (larger holes require too much material removal)
• Exception: EDM commonly makes large/deep holes in hard materials — a 0.2-inch hole was made in 2.9-inch thick carbide in 49 minutes

EDG — Electrical Discharge Grinding

A specialized variant using a graphite wheel as electrode (up to 12 inches diameter by 6 inches wide). The wheel is dressed to the required profile and transferred to the workpiece as it traverses past — the wheel rotates but does not touch the work. Primary use: complex profiles on polycrystalline diamond cutting tools and shaping carbide tooling.

Iron and Steel Castings — Shaping Metal from the Molten State

The first time the practitioner watched a casting being poured, he understood why foundry work is called an art as much as a science. Molten metal at thousands of degrees, flowing into sand molds shaped around wooden patterns — and the final part depending on factors from shrinkage allowances to carbon content.

The Four Basic Types of Cast Iron

Cast irons contain more than 2% carbon and 1 to 3% silicon. The mechanical and physical properties depend on the shape and distribution of free graphite and the type of matrix surrounding the graphite particles.

Gray Cast Iron

Characteristics:

• Carbon content: 1.7 – 4.5%
• Silicon content: 1 – 3%
• Excess carbon exists as graphite flakes → produces the dark-colored fracture
• Easily cast into complex shapes
• Readily machined
• Excellent damping capacity

ANSI/ASTM A48-76 Classifications:

The prefix number indicates minimum tensile strength in thousands of psi (20 = 20,000 psi, 25 = 25,000 psi, etc.).

White Cast Iron

• Nearly all carbon in combined (cementite) form
• Named for its silvery-white fracture
• Very hard, very brittle — ductility is practically zero
• Compressive strength: Usually > 200,000 psi (vs. 65,000 – 160,000 psi for gray iron)
• Sharp corners and thin sections → material failures in foundry
• Primary use: Production of malleable iron castings and applications requiring maximum wear resistance

Chilled Cast Iron

Gray iron castings with wear-resisting surfaces of white cast iron, produced by using metal chills in the mold for rapid cooling. The rapid cooling forms cementite and white cast iron at the surface while the interior remains gray iron.

Alloy Cast Iron

Contains alloying elements (nickel, chromium, molybdenum, copper, manganese) in sufficient amounts to change physical properties. Machinable versions achieve tensile strengths up to 70,000 psi or higher.

Common applications: Automotive cylinders, pistons, piston rings, crankcases, brake drums, machine tool castings, certain dies, crushing/grinding machinery, high-temperature components.

Malleable Iron Castings

Produced by annealing (graphitization) of white iron castings. The process creates temper carbon — graphite in compact rounded aggregates.

Production process:

1. Produce hard, brittle white iron from pig iron and scrap
2. Place in furnaces
3. Slowly increase temperature (~50 hours) to 1,650–1,700°F
4. Slowly cool (~60 hours)

ANSI/ASTM A47-77 Grades:

Cupola Malleable Iron (ANSI/ASTM 197-79):

• Min. tensile: 40,000 psi
• Min. yield: 30,000 psi
• Min. elongation: 5%
• Well suited to galvanizing

Pearlitic Malleable Iron Grades (ASTM A 220-79):

Ductile (Nodular) Cast Iron

The distinguishing feature: graphite is present in ball-like (spheroidal) form instead of flakes. Adding small amounts of magnesium- or cerium-bearing alloys produces this structure.

ASTM A 536-80 Grades:

Key advantages of ductile iron:

• Toughness intermediate between cast iron and steel
• Shock resistance comparable to mild carbon steel
• Good pressure tightness under high stress
• Can be welded and brazed
• Can be softened by annealing or hardened by normalizing
• Surface hardening by flame or induction methods is feasible
• Machined with the same ease as gray cast iron

Steel Castings

Especially adapted for parts that must withstand shocks or heavy loads. Stronger than wrought iron, cast iron, or malleable iron, and very tough.

Carbon Steel Casting Categories:

Casting Methods

Green-sand molding: The most common method. Sand mixed with binder is packed around a two-part pattern. The term "green-sand" means the binder is not cured by heating or chemical reactions.

Shell molding: Invented by Croning (Germany). Uses a resin binder to lock sand grains in a 1/4 to 3/8-inch thick layer. Provides better dimensional accuracy and surface finish than green-sand.

Other methods:

• Centrifugal casting
• Permanent mold casting
• Die casting
• Investment (lost-wax) casting

Pattern Materials and Shrinkage

Pattern woods ranked by application:

Critical insight on shrinkage: A straight round steel bar requires ~9/32 inch per foot shrinkage allowance. The same bar with large knobs on each end requires only 3/16 inch per foot. With large flanges at each end, only 7/64 inch per foot. Shape dramatically affects shrinkage — always get values from the foundry producing the casting.

Die Casting

Die casting forces molten metal into metal molds under pressure. Two process types:

• Hot-chamber process: For zinc, magnesium (low melting point alloys)
• Cold-chamber process: For aluminum, copper alloys (higher melting points)

Die casting alloys and their properties:

Precision Investment Casting

Investment casting uses expendable wax patterns joined to wax runners, coated with refractory material, then heated to remove the wax — leaving a precise ceramic mold.

Capabilities:

• Extremely intricate contours, interior and exterior
• Surfaces that couldn't be machined readily (or at all)
• May eliminate machining entirely or reduce it to a minimum
• Quantity range: A few pieces to thousands of duplicates
• Materials: Metals too hard to machine, high-temperature alloys, turbine blades

Extrusion of Metals — Pushing Metal Through a Die

The Basic Process

Extrusion squeezes a solid slug of metal from a closed container through a die — like dispensing toothpaste from a tube. During extrusion, compressive and shear forces are developed (no tensile forces), allowing heavy deformation without fracturing.

Extrusion methods:

Temperature ranges for hot extrusion:

Pressures range from 5,000 to over 100,000 psi.

Minimum cross sections and thicknesses:

Surface finishes achievable:

• Aluminum and magnesium: Better than 30 µin. rms
• Most steels and titanium: 125 µin. rms
• Minimum corner and fillet radii: 1/64 inch (aluminum/magnesium); 0.030 inch corners, 0.125 inch fillets (steel)

Cold extrusion advantages: No oxidation, high mechanical properties from cold working, narrow tolerances, good surface finish, and fast extrusion speeds. Products include collapsible tubes, aluminum cans, fire extinguisher cases, shock absorber cylinders, automotive pistons, and gear blanks.

Powder Metallurgy — Building Parts from Dust

The Process

1. Compress powdered metals (brass, bronze, aluminum, iron) in accurately formed dies
2. Sinter the "green" compressed pieces in a controlled-atmosphere furnace at high temperatures
3. Optional: Size or re-press, and apply supplementary heat treatments

What Powder Metallurgy Can Do That Other Processes Can't

• Parts with irregular curves, eccentrics, radial projections, or recesses
• Irregular holes, keyways, flat sides, splines, or square holes that are not easily machined
• Tapered holes and counter-bores
• Controlled porosity from 5 to 50 percent (for self-lubricating bearings, filters)
• Axial projections up to one-quarter the length of the part

Limitations

The difference in achievable tolerances between diameter and length is due to the elasticity of the powder and spring of the press.

Briquetting Tool Design

• Dies and punches: High-speed steel recommended
• Strippers and knock-outs: Oil-hardening steel
• Dimensional tolerances: 0.0002 inch with super-finished surfaces
• Wear mitigation: Carbide inserts, chrome plating, or highly resistant die steels
• Design rules: Use corner radii, fillets, and bevels — avoid sharp corners, feather edges, threads, and re-entrant angles
• Dimensional changes: Allowances must be made for growth after pressing and shrinkage or growth during sintering

The Joining Spectrum

the practitioner's second year brought him into the joining shop, where he quickly learned that the choice between soldering, brazing, and welding isn't just about temperature — it's about what the joint needs to do.

Soldering

Soldering employs lead- or tin-base alloys with melting points below 800°F. It provides a convenient joint for sealing and electrical contact, often combined with mechanical fastening (staking, crimping, folding).

Fluxes for soldering:

Soldering specific metals:

• Aluminum: Requires 550–770°F (vs. 375–400°F for common metals). Two methods: flow soldering (flux dissolves oxide) and friction soldering (mechanical abrasion under molten solder). Solders contain 50–75% tin with remainder zinc.
• Magnesium: Not ordinarily soldered. Used only for filling surface defects. Solder options: 60% Cd / 30% Zn / 10% Sn (melts at 315°F) or 90% Cd / 10% Zn (melts at 500°F). No flux — use mechanical abrasion.
• Stainless steel: Difficult due to tenacious oxide film and low thermal conductivity. Requires large soldering iron. Muriatic acid saturated with zinc is the standard flux. Flux residue removal is critical to prevent joint failure.

Ultrasonic fluxless soldering uses ultrasonic vibrations to penetrate surface films, eliminating flux entirely. Works on aluminum, copper, brass, silver, magnesium, germanium, and silicon.

Brazing

Brazing uses a non-ferrous filler metal with melting point below the base metal but above 800°F. The filler wets the base metal and flows between close-fitting surfaces by capillary action.

Seven standard brazing filler metal classifications:

1. Aluminum-silicon (BAlSi) — For aluminum alloys; joint clearances 0.006–0.025 inch
2. Copper-phosphorus (BCuP) — For copper and its alloys; clearances 0.001–0.005 inch; not for ferrous or nickel-base alloys
3. Silver (BAg) — For most ferrous and nonferrous metals (except aluminum and magnesium); clearances 0.002–0.005 inch
4. Nickel (BNi) — For stainless steels, heat-resistant alloys; suited to vacuum systems
5. Copper and copper-zinc (BCu, BCuZn) — For various ferrous and nonferrous metals
6. Magnesium (BMg) — For magnesium-base metals
7. Precious metals (BAu) — For iron, nickel, and cobalt-base metals requiring oxidation/corrosion resistance

Brazing flux selection guide:

Methods of supplying heat for brazing:

• Torch brazing: Direct flame application — most common for manual work
• Induction brazing: Eddy current heating from an electric coil — quick and clean
• Furnace brazing: Controlled atmosphere for mass production
• Vacuum furnace brazing: For stainless steels, heat-resistant alloys, titanium, refractory metals — no flux needed

Welding — The Four Processes That Account for 90% of Arc Welding

The Big Four:

Effects of alloying elements in welding electrodes:

GMAW — The Most-Used Welding Process

The two most common low-carbon steel electrodes:

Critical warning: When welding galvanized steel with GMAW, zinc coating reacts with silicon in the electrode, causing minute welding cracks. Use an electrode with the lowest possible silicon content (E70S-3).

FCAW — The Productivity Champion

Flux-cored arc welding produces spray-type transfer at lower currents than MIG spray transfer. The higher current density (due to central flux core reducing cross-sectional area) provides improved weld penetration potential.

Advantages over other processes:

• Fill passes completed in 30–50% less time than MIG short circuit and SMAW
• Slag serves as a mold for vertical-up and overhead welds
• Less operator skill required for vertical-up and overhead positions
• Open arc — continuous energy, increased weld fusion potential

Electron-Beam Welding

Uses voltages between 25 and 200 kV to accelerate electrons to 30–70% of the speed of light. Beam power can reach 100 kW with power densities up to 10⁷ W/in².

At these densities, an electron beam can penetrate steel up to 4 inches thick and form a vapor keyhole. Most efficient at high vacuum (10⁻⁶ to 10⁻³ torr), minimizing contamination by oxygen and nitrogen.

Laser Technology — Light That Cuts, Welds, Drills, and Treats

Common Industrial Laser Applications

Beam Focusing — The Physics of Precision

Spot diameter: $d = f \times \theta$ (focal length × beam divergence)

Power density: $H = \frac{4P}{\pi d^2}$

Depth of focus: $Z = \pm \frac{\pi d^2}{4\lambda}$

A CO₂ laser (10.6 µm wavelength) using the same focal length lens produces a focused spot ten times larger than a Nd:YAG laser (1.06 µm wavelength). Power density varies with the square of the area — a small change in spot size produces a 4× change in power density.