A new system from Martinmechanic, which has been developed for overmolding electronic components, is the size of a stately family home. In the MAP242236, five precisely coordinated work cells work hand in hand on a floor area of 130 square meters, with a total of nine Stäubli robots at work. The manufactured components are used to assemble the housings of circulating pumps for the electronics industry. Seven four-axis Scara TS 80 robots are used for this because of their long reach at maximum speed, another four-axis Scara TS 60 robot and a six-axis TX 200 robot. Three workpiece carrier circulation systems and four punching units have also been integrated into the cell.

Belt cycle time of 20 seconds
The automation system consists of pre-assembly, assembly for the injection molding machine, a cooling cell, the test cell and the palletizing cell. Five robots are used in pre-assembly alone for the production of punched sheets and contact plates. The two servo-electric presses have a punching force of 40 tons, the two pneumohydraulic presses 20 kilonewtons. Because work is carried out in parallel, two workpiece carrier circulation systems are used to eliminate the entry and exit times of the workpiece carrier. Each belt has a cycle time of 20 seconds.

So the robot always has something to do. Because if it can't deposit on the first belt, it goes straight to the second and vice versa. The strip material for the four different sheet metal parts is unwound via reels. Once the components have been punched out, the robot always places them in parallel in the workpiece carriers, each with two cavities, which travel on the circulation belt. The complete setting pattern consists of the punched sheet, contact sheet, the contact unit vaporized with gold for optimum conductivity, the solder pin and five copper discs. The latter are fed in via a conveyor bowl.

Overmolded parts carefully cooled down
The six-axis robot uses its quadruple gripper to remove two complete setting patterns from the workpiece carrier in order to insert them precisely into a pendulum table of the vertical injection molding machine. The injection mold is located on the underside of the machine and closes automatically so that the injection process can begin; it takes just 16 seconds.

The six-axis robot places the overmoulded finished parts in the rotary indexing table of the cooling cell, which continues to its second and third stations, where the temperature is lowered in each case. This prevents the material from warping. Only at the fourth station of the rotary indexing table are the overmolded copper discs punched out to their final dimensions in the middle after the cooling process. This enables maximum precision to be achieved.

Bad parts are rejected immediately
To avoid rejects as far as possible, parts that are not in order should be detected and rejected as early as possible. Image processing, which is installed above the parts to be inspected, is used to check whether the sprue in the center of the copper disc has been completely removed and whether there is any overmolding. A Scara robot picks up the overmolded parts and sorts out bad parts directly via a separate discharge belt. The good parts are deposited on the third workpiece carrier circulation system, which serves as a buffer between the cooling and test cell. Another Scara robot now places the good parts in the rotary indexing table of the test cell, which in turn has eight stations and cycles in 40 seconds - it works on five components simultaneously. These are first turned and prepared in the assembly direction. A high-voltage test is carried out at the second station. To do this, the test head is lowered onto the solder pins to perform a short circuit test. Parts that do not pass this test are ejected from the ongoing process by the robot.

Two capacitors are fed to the component at the third station. The Scara robot removes one capacitor at a time from the carrier tape and inserts it into the contact pin bending station. The contact pin is carefully pre-bent and deflected so that the capacitor can be pressed into the housing. The contact pin is then pressed into the contact fork. At the fourth, fifth and sixth stations, the contact pins of the respective capacitors are welded to the contact fork. The low-voltage test measures the voltage and discharge current at the seventh station. If the values meet the manufacturer's specifications, they are given their specific data matrix code at the eighth and final station.

Siemens controls "fail-safe"
The components then return to the first station of the rotary indexing table, where they are removed by the robot and placed twelve at a time in a blister. Finally, a palletizing and depalletizing cell from Martinsystems' standard range takes over the blister handling.

The carefully devised PLC control of the entire system is handled by a Siemens S7-1515F; the "F" stands for "fail-safe". The operator uses the mobile, wired KTP700 panel for this purpose. The entire system took twelve months to develop and build. pb