25 Jan 2019
Turned parts subcontractor, Empire Manufacturing, bought its first vertical machining centre (VMC), a Leadwell V32i, in April 2015. Its purpose is to fulfil regular orders placed by an existing customer for rotational parts requiring a lot of additional milling, too much for the eight Star sliding-head turn-mill centres on site to tackle economically.
The EN16T steel dowel component, measuring 20 mm in diameter by 40 mm long, is a price-sensitive part for a pump. Manufacturing cost had to be minimised to win the business, which meant presenting a large number of components simultaneously to the VMC spindle.
Multi-loading decreases the load/unload time and the number of tool changes per component, reducing spindle downtime. A process is therefore more efficient and capacity is increased by utilising more of the machine envelope. The operator is able to walk away from the machine to carry out other tasks and the manufacturing cost per part is reduced.
Hoddesdon-based Empire Manufacturing turned to workholding specialists 1st Machine Tool Accessories for a solution. After analysing the application, it suggested using two US-made Chick System 5 1550 Qwik-Loks, but not fitted with the standard, dual station jaw sets. Instead, they are equipped with solid aluminium faceplates that act like zero-point pallet changers and repeat within microns.
With two machined recesses on the undersides that snap onto the Qwik-Lok slide assembly in the bases, the faceplates are secured in a matter of seconds. The solid, high tensile aluminium faceplates are fully machinable, facilitating bespoke fixture designs. The system is completely sealed against ingress of swarf and coolant.
In this application, the faceplates incorporate Mitee Bite Uniforce machinable clamps, also from the US, which were machined with semi-cylindrical recesses to hold the dowel components after they have been turned and ground. Clamping of each component is achieved by tightening a single M6 socket screw, which applies a pressure of 6,675 N, more than sufficient to secure the dowel components for roughing, finishing and chamfer-milling around the circumference.
Two faceplates securing a total of 120 components are presented to the spindle and profile-milled in a 40-minute cycle on the VMC. The faceplates are then removed and replaced with two identical faceplates that have been pre-loaded outside the machine with 120 steel dowel blanks whilst the machine has been running.
Faceplate exchange takes a couple of minutes, resulting in minimal machine downtime. Subsequently, releasing 120 dowels from their Mitee Bite clamps, counting and packing them into boxes and reloading the faceplates with fresh dowel blanks ready for the next cycle takes 15 minutes. The operator therefore has around 25 minutes of walk-away time to complete other tasks during every cycle.
Stuart Wade, a director of the family-run subcontract machine shop commented, “If we were to secure the round dowels in two conventional vices side by side on the VMC table, we could only mount four of them on the machine, as a third dowel in a vice jaw would almost certainly spin as it is milled.
“Using two Chick Qwik-Loks with dual station jaws we would double the number to eight dowels, but that is still a fraction of the number that we can put under spindle using the Chick faceplates and Mitee Bite clamping arrangement recommended by 1st MTA.
“It is not only an effective solution but an economical one as well. We were shocked at the £20,000 price of a zero-point clamping system we looked at early on, whereas the 1st MTA package cost only £8,000.”
Empire Manufacturing now has a highly capable and repeatable system for manufacturing 8,000 to 10,000 pump dowels per month over a single 9-hour shift plus 40 minutes unattended running at the end of each day. The ± 0.1mm tolerance on the milled periphery is easily held, as is the required high standard of surface finish.
After a small production backlog has been eliminated, the VMC will complete the current on-going dowel production quantities in two weeks per month. Other work will be taken on to fill the remainder of the machine time, helping to amortise the capital investment even faster.
Two views of a pair of Chick faceplates with a total of 120 dowels secured to two System 5 Qwik-Lok bases on the table of the Leadwell VMC.
Close-up of the 120 dowels after they have been milled on the VMC.
One of the faceplates has been removed, illustrating that the Qwik-Lok base and slide assembly is completely sealed against ingress of swarf.
The finish machined dowels are removed from the Mitee-Bite clamps using an M6 socket wrench, as it is faster than using the torque spanner that initially ensures that the components are secured firmly for milling.