Lego blocks bad NC code thanks to VERICUT

By Thore Dam Mortensen,

Within the Engineering, Prototypes & Tooling department of Danish toy maker LEGO, simulation of all NC programs ensures that the engineers can sleep at night without worrying about crashed spindles and costly production downtime.

Getting a good night’s sleep can be difficult: especially when you are involved with the production of complex moulds and dies and face the daily risk of a costly and damaging collision between a machine tool spindle and the tool material. This was the scenario at the Billund, Denmark, headquarters of world-renowned toymaker LEGO Group, until the company installed the advanced simulation software VERICUT, supplied by UK-based CGTech, in its Engineering, Prototypes & Tooling department.

“With the traditional simulation that many CAM packages are capable of there are certain parameters that you cannot take into consideration,” says project manager with LEGO Engineering, Prototypes & Tooling, Christian Wissing Kruse. “Often the programs do not consider the individual CNC machine’s kinematic properties and most programs simulate internal CAM movements and not post-processed data. These shortcomings can be fatal if, for example, you plan to operate with the machine’s spindle in close proximity to the workpiece.

“If we crash a spindle on a CNC-machine it means up to a week of missing production on the machine in question. First, we need a service technician, then we need to assess the damage, and then we need to realign the machine. When that is done, we need to replace the spindle with one we have in reserve or we need to order a new one. This is what we want to avoid by simulation of all our NC programming,” says Christian Wissing Kruse.

“We have measured our CNC machines, so VERICUT knows them inside and out. When the final NC program has been written, we send it to a shortcut on the PC’s desktop from where a simulation is conducted on a dedicated PC-server through a system of Windows batch-scripts and VB-scripts. We do not need to watch the program as it is simulated and when the simulation is complete, an email message is sent to the relevant person with a green ‘go-ahead’ or red ‘stop’ in the message field.”

The simulations demand a serious amount of computing power so it makes sense to use a dedicated server, allowing users to work on other tasks on their own workstations without their capabilities being inhibited by a massive CPU-usage. “This is necessary as the simulations often run for up to six hours. And, even if it does take a lot of time to do the simulations, it is time well spent as a collision may cost a ruined spindle. Not to mention a full week of production for the remedial work to be carried out,” says Mr Kruse.

“The simulation may take up to six hours but also ensures, to a degree of certainty of 99.9 per cent, that we do not risk a collision,” says Christian Wissing Kruse.

“If we do get a red ‘stop’, we open the log-file to see in which line and with which tool there is a risk of collision. We then directly edit the CAM program or we do a bit of detective work with Cimco Edit to locate in which CAM operation the fault was generated. All in all, our simulation solution helps us sleep at night,” Mr Kruse confirms.

When the simulation is done, an email is sent to the relevant employee: if it is green in the message field everything is OK; red means that there is a fault or risk of collision somewhere in the progra

To ensure optimum computing power the investment on top of the simulation software included a T 7400 Dell workstation with one CPU, with extension possibilities for two CPUs, as well as 16 gigabytes of RAM. The hardware price tag was nearly £7,000 and the software tag reached £11,500 as LEGO had certain software modules already.

”My estimate is that a software solution such as ours will cost you around £23,000. Considering, however, that a spindle alone will set you back £12,000 it is certainly money well spent,” Mr Kruse states.

Software and computer-hardware is only one side of the equation, though, and the department has over the years invested in a very efficient range of eight CNC machines. Says Mr Kruse: “We have a strategy of standardising our workshop based on a common technology platform, much the same as the whole company’s production philosophy. We have chosen to buy Mikron CNC machines and currently have three 3-axis VCP 600, a 3-axis HPM 600 and, as the jewel in the crown, four 5-axis HSM 400U

“We bought the first 5-axis machine in 1999. It never actually ran at its optimum, but on the other hand it provided us with some very valuable experience. In 2002, we installed our first Mikron machining centre and from thereon really built our 5-axis experience.”

Like the rest of the LEGO Group, the Engineering, Prototypes & Tooling department has seen an all-encompassing restructuring and streamlining of processes and tasks during the past couple of years. The overall objective has been to align the whole Group with the market, to be better prepared for the frequently abrupt changes.

“We have focused on Lean Principles and the best sign of that is actually in the tool shop where things are a lot tidier and cleaner than just a few years ago. All tools, for example, are always placed where you need them,” says Mr Kruse. “Every Thursday we hold a large meeting, nicknamed Morning Prayer, where all team managers and process managers in the Lean-Project gather and prioritise the suggestions for process improvements. These meetings ensure that we each focus on ‘Lean manufacturing’ and ensure that we keep Engineering, Prototypes & Tooling competitive when it comes to developing and producing moulds and dies for our companies worldwide.”