Mould tool methodology

A ProtoTrak turret mill was the first of several CNC/manual mills and lathes to be supplied by XYZ Machine Tools.

However, Sterling Products' latest investment is a full CNC XYZ 1010 VMC equipped with Siemens 810D ShopMill control. The 15kW (20hp)/8,000rpm vertical machining centre was installed some 18 months ago and, according to Mr Bowyer, ‘is providing the versatility and reliability that we need'.

Founded in 1992 and located in the historic Somerset town of Bridgwater, Sterling Products specialises in the design and manufacture of moulds used to vacuum form plastics packaging for a wide range of industries. The seven strong company opts to machine moulds from solid rather than source raw castings to retain complete control of the production process. By not having to wait for raw castings to be delivered, the company reports it can save up to 48 hours – which is vital as it is often working to tight deadlines.

Prototype moulds machined from model resin are used to produce sample packaging in-house, which is then submitted to the customer for checking and approval. This process includes ensuring that vacuum formed food containers, for example, when stacked prior to use can easily be separated, and transit trials to check that individual containers and their contents can be stacked securely and transported safely. Once a packaging design has been finalised, a production mould can then be machined in aluminium.

"Having a machine with the capacity of the 1010 VMC allows us to load, say, a dozen workpieces on its 1,200mm by 450mm table, download the required programs and then run the machine unattended overnight and at weekends," says Mr Riddle. "We come in to find that the job, which may involve machining several identical moulds for one customer or any combination of moulds for several customers, has been completed and the machine has turned itself off. This is how we stay competitive and maintain our business at a comfortable size."

The 1010 VMC's 24 station toolchanger has a 2.5 second tool change time (tool to tool) and features extra wide hardened and ground box slideways for maximum rigidity and vibration absorption. X, Y and Z travels are 1,010mm, 504mm and 540mm respectively, with rapid feed rates of 24m/minute on all three axes.

Simple conversational programming of the Siemens ShopMill control ensures the minimum of operator keystrokes, with canned cycles catering for common machining functions such as contour pocketing, and no need for G coding knowledge. Checking everything is correct before machining is equally simple: the control features a line trace view and a simulation package that allows the operator to see exactly what is going to be machined before pressing the ‘Cycle Start' button. Having been introduced to CADCAM at an XYZ open day, anything other than relatively simple moulds or general machining work is programmed offline. Using a network link from the PC to the machine, programs can be copied to the control system's internal storage or executed directly from the computer's hard drive. And rather than store NC programs, the original model information is kept on file to provide the basis for new programs that take account of any subsequent design tweaks.

Ex-apprentices themselves, Messrs Bowyer and Riddle are firm believers in the apprenticeship system and have helped a number of young people over the years to gain engineering skills and experience. One of the current team is a former apprentice with seven years service and another is in his first year as an apprentice, attending day release at Bridgwater College.

"The practical side of mould making has been made less difficult in recent years with the wider use of CADCAM and CNC machine tools," says Mr Bowyer, "and the ease with which the XYZ machines can be programmed and operated is a case in point. However, mould tool making is still a very demanding discipline and one where there is an increasing requirement for more academically-based knowledge."

XYZ
www.xyzmachinetools.com