What is metal stamping?

Metal components can be fabricated in a mass volume by a variety processes such as sand casting, metal die casting, machining etc. One of the more economical and common processes used for making sheet metal parts is by metal stamping.

Metal stamping process, which in general involves taking a flat raw metal sheet, cut and form or bend it into the required shape and size. Product such as Mounting brackets, casing, electronic connectors for instance. metal stamping process is the most cost-effective process that permits metal parts to be manufactured at a high production rates. Production speed can be ranging from 40 to 2000 parts per minute.

In a metal stamping process, a sheet of metal stock material in fixed thickness and width is introduced into a stamping press. The stamping press can be either a mechanical or hydraulically driven depend of it process requirement. A stamping tool in two half are mounted on the press machine, the upper part of the tool is so call punch and the lower part is called die. The punch and die will be moving up and down with the press machine ram to cut and form the stock material into the final shape and size.

Press machine can be as small as 10 tons and as large as 800 tons. The mechanical driven press are usually run in a faster speed than the hydraulically driven. The Hydraulic press usually provides heavier tonnage than a mechanical one.

In general, The sheet metal has been cut to the required shape and size by a blanking tool and subsequently transfer to other presses and tools to perform the secondary process such as piercing, forming or bending, the process will be repeated under the final form is achieved.

The whole operation is done by manually loading and unloading, in some cases, robot transfer arms are installed in the production line to replace all manual work, all metal parts are transfer by robot. The tool designed in such, we called it a transfer tool.
Because the single transfer process requires frequent changing of tooling or press machine, it is usually not economical to runs large volume production batch. A progressive tool is introduced to runs the complex component within one single stamping tool and press.
A progressive tool consists of all the operations within a tool, imagine, all single stamping tools are to align in a fix distance within the tool. Each tool is called a station. Raw material in coil form will than introduced into the tool by either a mechanical or electronic control feeder to feed sheet metal in the tool.

The different between a transfer tool and a progressive tool is usually the transfer tools are larger in size, it may requires a few press machines at one time. As for the progressive tool, tooling is smaller in size and runs on only one press machine.

Two location pins in each station locate the metal part precisely to ensure the accuracy of the stamped parts in a progressive tool. The location pin we called it a Pilot pin.

Progressive tool is commonly used in the metal stamping industries.

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Die protection system in high speed metal stampings

Die Protection system is used to protect your progressive die in the case of any unexpected event. These events can be misfeed, strip buckle, double hits, slug up, broken punch etc.

A mis-feed pilot is used in most of the tool shops for tool protection since the last four decades. Today, many conventional tool shops are still using it. The micro switch connected to the machine e-stop. The micro switch cut off the power supply and eventually stops the machine when the pilot activated the micro switch when misfeed is detected. This method usually applied to low speed conventional stamping with 50-100 spm.

In today market, stamping machines are running in much more faster speed. Misfeed pilot is no longer sufficient in die protection. Double hit, slug up and strip buckle is no way to be detected by this method.

A Photoelectric fork light sensor is commonly used for reel to reel high speed stamping industry. This fork sensor is a through-beam photosensor with a pre-aligned emitter and receiver permanently housed in a U shaped cast metal case. The sensor is installed either within the tool or at the end of the tool, to detect either a hole or the edge of the strip, it is programmable to count number of passes during one machine cycle according to number of out the tool is running. The counting is done during the feeding of stock material before the punching stroke take place. Electronic signal will pass to the controller to stop the machine when the actual counting does not match the pre-set number. As such, misfeed can be detected immediately before the punching ram is actually descended down. It is a great way to detect misfeed in the high speed stamping environment. However, this method is not able to detect slug up and broken punch effectively.

Another type of die protection system is widely used in the Precision metal stamping industry industry, a sensor is mounted at the die plate or spring stripper to monitors the gap between the stripper and die surface. This gap can be as fine as .00004 inches (1/1000mm), By monitoring these subtle deviations in stripper position or die height, it can detects misfeeds, pulled slugs, double hits or other abnormal conditions. The protection system can be applied to any stamping operation with speeds up to 2500 machine cycles per minute (SPM).
Once the machine is at production speed, the upper and lower limits are automatically adjusted based on your stamping process. Unfortunately, the detection will happen always after the punch and die is in contact. In short, damages had already done to the tool.

The combination of both methods in one tool is advisable for die protection in the high speed stamping industry.

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