Transfer press stamping (referred to in the sources as 搬送プレス加工 or トランスファプレス加工) is an automated high-efficiency metal forming process where raw material (either coiled strip or pre-cut blanks) is fed into a press, and individual, detached workpieces are automatically moved through consecutive die stations in a single press or a series of parallel presses to produce a finished part.
Unlike progressive die stamping, where workpieces remain attached to a continuous metal carrier strip throughout the process, transfer press stamping processes completely independent, singular workpieces at each station.
1. How It Works (The Transport Mechanism)
The heart of the transfer process lies in its automated transport mechanism, known as the transfer feed (トランスファフィード):
- Feed Bars and Gripper Fingers: Symmetrically placed feed bars run parallel to the press bed. These bars are equipped with custom-designed gripper fingers (グリップフィンガ) or suction cups tailored to the shape of the part.
- The Motion Cycle: Synchronized with the vertical stroke of the press slide, the gripper fingers perform a precise sequence of movements to clamp the workpiece, advance it by one feed pitch, release it into the next die, and return to the starting position.
- 2D vs. 3D Transfer Motion:
- 2D Transfer (2次元): The fingers only move in two axes—clamping/unclamping (in/out) and feeding/returning (forward/backward). The workpiece slides along lift rails or slide plates.
- 3D Transfer (3次元): The fingers move in three axes—clamping/unclamping, lifting/lowering, and feeding/returning. This allows the workpiece to be lifted completely clear of the lower die, advanced, and lowered into the next station, which is essential for complex shapes and preventing surface scratches.
2. Main Advantages (長所)
- High Safety (安全性高 / “No-Hand-In-Die”): Because the feeding, transferring, and ejection of parts are entirely automated, operators do not have to put their hands anywhere near the dangerous slide area, resulting in an exceptionally safe working environment.
- Excellent Material Yield (材料歩留りが良好): Since the workpieces are completely detached from one another, there is no need to consume material on a continuous carrier skeleton. Blanks can be nested tightly together prior to feeding, significantly reducing scrap and lowering raw material costs.
- Complex and Side Processing (加工の自在性): Because the parts are loose and independent, they can easily be rotated, flipped, or subjected to horizontal cam actions. This makes operations like side piercing, side-trimming, or complex forming highly feasible, which would be extremely difficult inside a progressive die.
- Deep Drawing Advantage (適合深絞り): Transfer stamping is outstanding for deep drawing. It allows consecutive drawing stages to be completed progressively in one automated cycle, which often eliminates the need for time-consuming intermediate annealing (中間焼鈍).
3. Key Challenges and Limitations (短所)
- High Initial Equipment Cost (設備高価): Automated transfer presses, feed bars, and customized finger configurations represent a massive capital investment compared to manual single-hit presses or standard roll-fed progressive lines.
- Stricter Die Design Requirements: All the individual dies installed in the press must be engineered to align perfectly. Specifically, the die heights (shut heights) across all stations must be meticulously matched.
- Transfer-Specific Phenomenons (トランスファ特有の現象): Continuous automated transfer introduces physical variables that must be monitored:
- Inertia and vibrations can cause positional displacement (位置ずれ) of parts during high-speed transport.
- Lubricating oils can cause parts to slip (滑り移動) out of grippers.
- High-speed continuous contact can cause die heating and seizure (発熱焼付).
- Small metal slivers and slugs (微量かす) can accumulate, causing surface defects if not managed.
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