Automotive Parts Manufacturing Process

Presses are the Starting Point of Automotive Parts

Almost all steel parts in a single car are made by presses. Door panels, seat frames, various brackets, oil pans, and muffler covers are all made this way. This is why press subcontractors are concentrated around the final assembly plants in Ulsan, Busan, and Changwon.

A press is a process where a sheet is placed between dies and subjected to a sudden large force to form a shape. Since it doesn't involve cutting away material, it's fast and results in less material loss. However, two things come with it. The die determines the quality, and if you get hurt, you get hurt badly.

1. Types of Press Processes

Blanking and Piercing are the Same Action, Different Purposes

Press the punch onto the sheet and remove it — the action is the same

The piece that falls off is the product → **Blanking** (the die determines the product dimensions)
The sheet with a hole is the product → **Piercing** (the punch determines the hole dimensions)

Depending on which side is the product, the dimension standard becomes either the punch or the die. If you mix this up during die maintenance, the dimensions will be reversed.

2. Clearance — the Value that Determines Burrs

The gap between the punch and the die is called clearance. This single value largely determines the quality of the product's cross-section.

       ┌──────  Rollover    The part that is pushed and rounded
Sheet  │──────  Burnish     The smooth surface pushed
Thickness│
       │──────  Fracture    The rough surface that is torn
       └──────  Burr        The sharp edge pushed out on the opposite side

Side Clearance = Sheet Thickness × Ratio (5~10% depending on material)

For soft steel t = 2.0mm with 6% applied
  Side Clearance = 2.0 × 0.06 = 0.12mm

If you punch a φ20 hole with piercing:
  Punch = φ20.00        (determines the hole dimension)
  Die = 20.00 + 0.12 × 2 = φ20.24

> If you hear people on the shop floor say "the burr is getting worse lately," it's usually because die wear has caused the clearance to widen. Burrs are not just an appearance issue. They can tear rubber seals during assembly, cut workers' hands, and leave protrusions after painting.

3. Drawing — the Most Difficult Process

This process pulls a flat sheet into a cup or box shape. The material must flow in, and the blank holder presses to control that flow.

If the blank holder force is weak → the flange folds = wrinkle
If the blank holder force is strong → the material doesn't flow = crack

Only the narrow range between these two is the "formable area"

• If the depth is too great, you can't form it in one go. Redrawing is used to form it in 2–3 stages.
• If the corner R is too small, it will crack there. Don't arbitrarily reduce the R on the drawing.
• If lubrication is interrupted, the material sticks to the die, causing scratches and galling.
• After drawing, you must trim to cut off the excess flange.

4. Springback — the Bended Angle Returns

Metal retains some elastic components even after bending, so when the die is opened, the angle slightly straightens. This is called springback.

Target bending angle 90 degrees
First trial (test press) measured 93 degrees → springback 3 degrees

Die adjustment: overbend to 87 degrees
Second trial measured 90.2 degrees → confirm tolerance and finalize production conditions

> Recently, the proportion of high-strength steel in car bodies has been increasing due to lightweighting and collision safety. If you use the same die adjustment method as with soft steel, the angle won't come out right. If the material grade changes, die adjustment is needed again.

Solutions include overbending, bottoming (bottoming), maintaining forming pressure points, and adjusting the die shape.

5. Die Structure and Types

6. Safety — the Machine That Takes the Most Fingers

Most press injuries occur when a hand is inserted into the die. Because the scrap is caught, the product doesn't come out, or it seems like it can be touched just a little.

Safety Devices Must Match the Press Type

> Installing a light curtain on a mechanical clutch crank press without emergency stop function is useless. Even if the light is blocked, the slide continues to descend due to inertia. First, confirm what type of equipment you have.

The Distance of the Two-Hand Control Button is Critical

Safety Distance  D(mm) = 1.6 × (TL + TS)

  TL : Time (ms) from when the hand leaves the button until the emergency stop mechanism starts
  TS : Time (ms) from when the emergency stop mechanism starts until the slide stops
  ※ Use actual measured values from the equipment specification sheet and safety inspection report, do not estimate arbitrarily
  TS : Time (ms) for the slide to stop after emergency stop

Example) For a press with TL + TS = 200ms D = 1.6 × 200 = 320mm → The push button must be at least 320mm away from the danger limit

• The distance between the two buttons also has a standard (minimum internal distance of 300mm). This prevents one hand from pressing both buttons at the same time.
• Fixing a button with tape or material is a major accident waiting to happen.

Checklist for Die Replacement

• Power off + Lock Out / Tag Out (LOTO) — prevent others from turning it on
• Insert Safety Block — if hydraulic or pneumatic pressure drops, the slide will fall due to its own weight
• Confirm residual pressure
• At least two people, assign a signal person
• Confirm die weight and select sling/crane accordingly

Other Things

• U-shaped cover on the pedal — it's common for materials or feet to cause malfunction accidents
• Use a clamp to remove scrap inside the die. Never use your hands
• Presses are subject to safety inspections. The first inspection is within 3 years after installation, then every 2 years
• Disabling or invalidating safety devices is illegal

Common Mistakes Made by Newcomers