April 2021

36 n MACHINE BUILDING April 2021 www.drivesncontrols.com Cutting-edge cell assembles blades for Stanley knives B lack & Decker’s tool-making brand Stanley Tools wanted to improve the assembly of the blades for plastic-handled safety knives at a UK factory. The process involves the assembly of four intricate components: the handle, blade, sliding mechanism and blade fixing component. This assembly has historically been done by hand, but due to the high level of precision and repeatability required, and the global demand for its products, Stanley decided to automate the process to increase production yields and cut time-to-market. By commissioning a rotary assembly cell, it would be able to replace a repetitive manual process and achieve benefits such as improved productivity and quality. The assembly cell had to capable of producing safety knives with two different blade sizes – with widths of 9mm and 18mm – and to swap production efficiently between the two. To meet demand, it needed to achieve a cycle time of 20 parts per minute. The machine also had to be small enough to fit in an existing space at the production facility. Stanley Black & Decker awarded the contract to design and build the automated assembly cell to PCE Automation, which won the tender against international competition. The new cell was designed, manufactured and programmed at PCE’s Suffolk site. The machine is an eight-station rotary assembly cell. The blade handles are held in position on a central rotary assembly and various components, including the blades, are placed precisely to build up the final product. As the assembled knives leave the cell on a conveyor, they are inspected by a machine vision camera for quality control. Stanley did not want the cell to require constant overseeing by an operator. So hoppers are used to feed components into vibrating bowl feeders. The hopper feeds can keep the cell running for about an hour without an operator needing to intervene. The bowl feeders were produced by PCE’s sister company, Premier Bowl Feeders. Mitsubishi supplied Scara robots to perform the simultaneous pick-and-place (PnP) movements demanded by the application, efficiently processing intricate components from upstream bowl and linear feeders and placing them accurately. Introducing the knife blades into the assembly cell was a particular challenge. The two blade lengths are presented to the cell in stacks of 400. Because each blade is only 0.4mm or 0.5mm thick, it is tricky to pick-and- place them accurately. There was a real risk of the blades jamming and halting production if not positioned correctly, so it was critical to be able to pick one blade at a time and place it in the correct orientation. PCE solved this problem by using magnets to hold the blades. Grippers are used to pick-and-place all of the other components. These grippers were supplied by Festo, which also provided other equipment for the cell, including mini-slides, axes, cylinders, valves, and a CPX-AP-I decentralised I/O system which integrates IO-Link, high-speed data transfer to the cloud, and intelligent connections to a host PLC in one package. It acts as a single control network using one cable for all communications and power. In the Stanley application, it allows valve terminals and other components to be positioned flexibly around the cell – simplifying installation and cutting costs. Festo’s DGST mini-slides and grippers, work with its DFM guided pneumatic actuators to present the plastic components for assembly accurately and repeatably. After the knives have been assembled, a Cognex vision system carries out quality checks. Stanley’s new cell is said to meet all of its requirements. The company no longer needs to oversee the production process continuously, and can change efficiently between different product sizes. It has also achieved its desired rate of output, while maintaining stringent quality standards. n The hand-tool manufacturer Stanley has automated the intricate assembly of safety knife blades at a UK plant. The new cell has allowed it to boost production and quality, and cut time-to-market. Stanley is now producing its safety knives faster and without affecting quality following the commissioning of this rotary assembly cell