Initially founded as tool shop making moulds for sheet metal working, Sacel (Ozegna, Turin) is now a multifaceted enterprise, having expanded its core business to integrate its expertise in other areas: moulds for plastic materials, progressive dies for sheet metal, injection molding of plastics, laser welding and assembly. «Thanks to the know-how we have developed in a range of sectors – Sacel's vice-president Raffaella Caretto tells Plastix – we can now develop production processes tailored to every specific requirement. The cornerstone of all this is still automation, however, which allows us to guarantee quality production that is also highly competitive in terms of time and cost efficiency».
The punching grid is composed of eight circuits, obtained through the punching and bending of two copper pieces. These circuits are assembled inside the mold into which the PPS is injected.
A special project
Eighty-five per cent of the turnover of this Piedmont-based group is generated in the automotive sector, through a clientele comprised largely of tier-one suppliers of the major automobile manufacturers. One of these, Magna Electronics, has entrusted Sacel with the production process design and subsequent manufacture of a punching grid, a component that will be used in the starter motor of the radiator cooling system of several Volkswagen and BMW models. Made from galvanized copper and 40 percent glass fiber-reinforced PPS, it is a two-material component. Thanks to intensive work on the design (in collaboration with the customer) and on the development and construction of the moulds and dedicated production line, the components were being mass produced within a span of time of just a year. In 2012, around 80,000 per month were being produced, and the launch of a new plant is set to raise the production capacity further, to as much as 2.2 million per year by the end of 2013.
«The punching grid – explains Raffaella Caretto – is composed by eight circuits, obtained through the punching and bending of two copper pieces, which differ in shape and size. These circuits are assembled inside the mould into which the PPS is injected». It is therefore a complex component, whose realization requires different processing stations, all fully designed and robotized by Sacel technical staff. In automation terms, the process can be divided into two steps. The first, i.e. the punching of the metal parts, is a discontinuous process since it involves a step that has to be outsourced; the second, on the other hand, i.e. the overmoulding of the pieces with plastic, is fully automated.
View of the punching department. The process begins with the prepunching of two copper coils. The resulting pieces undergo a galvanic tin plating treatment.
The production line
«The process begins with the pre-punching of two copper coils» explains Raffella Caretto, showing us the production line. «These then undergo galvanic tin plating, a treatment carried out by a carefully selected subcontractor. Once they return to us, the material is punched again, to obtain the two different metal pieces mentioned earlier. After this, the pieces are loaded onto a rotary table located at the entrance to the automated station. A controlled axis Cartesian robot, equipped with suction grippers, picks up a pair of pieces at a time – these are fed to it by the movement of the rotary table – which it then deposits on the carriage of the press. Here the pieces are bent and separated, one into five circuits and the other into three. Thanks to the punching and bending of the pins on the machine it is possible to avoid piece deformation and damage, drawbacks that tend to arise with manual operations».
The company’s internal tooling department for the production of moulds for plastic and metal working is periodically updated with modern equipment.
Overmoulding with PPS
The separation and bending steps are followed by overmoulding of the pieces with PPS. This is carried out by a 150-ton Wittmann Battenfeld vertical injection moulding machine, mod. VM 150/210 V 1280R, specially developed for the moulding of engineering polymers and equipped with a two-station electric rotary table. Situated on the latter is a mould with 2+2 cavities. «The circuits – continues Raffaella Caretto – are picked up by a linear translation device which inserts them into the mould. The table then rotates through 180 degrees, moving the mould to the second station, where the overmoulding with PPS takes place. The correct positioning of the different circuits inside the mould is guaranteed both by sensors fitted in the cavities, which detect the presence of the pins, and by a control system which monitors the vacuum level of the robot's suction grippers. Any malfunctioning is signaled by an alarm, which stops the working cycle».
Drawing attention to the critical aspects of the process, Raffaella Caretto remarks «PPS is processed at higher temperatures than the other plastic materials that we generally work with: indeed, the polymer is injected at a temperature of 320 °C, while the mold is maintained at 145 °C. In order to avoid disrupting delicate balance of the whole cycle, we have installed a Wittmann Tempro Plus D pressurized water temperature controller set to 160 °C, complete with a control panel operating from the press. Raw material conditioning before processing is also quite a critical stage, and for this purpose we use a Wittmann Drymax E30/70 PDC dryer, in which the material is transported in a closed-loop circuit and the process temperature is increased to 180 °C».
Injection moulding department.
Close monitoring
«The punching grid – she goes on – must meet some extremely critical requirements. Therefore, we have implemented an in-line control system, which accomplishes a subset of rapid operations. The piece is moved into four positions to allow evaluation, by a Cognex viewing device, of a series of critical parameters, such as presence of flashes, completeness of the overmoulded parts, holes in the right places, correct bending of the metal pins and integrity. Once the check is complete, the pieces are carried out of the workstation on a conveyor belt and sent on to a cell for ultrasonic cleaning, a treatment that gets rid of any contaminations».
One very important aspect of the control procedure is its duration: indeed, even though a large number of parameters are checked on every single piece, what is more the Sacel technicians have nevertheless managed to make its duration match with that of the injection mould phase, which is just under 40 seconds. «Staying competitive in our market – comments Raffaella Caretto – means optimizing every tiny detail. This explains why we have made complexity the basis of our business model. For us, complexity means the ability to concentrate, within the company, various advanced technologies and to integrate them into the development of plants for the production of hi-tech components».
