Bill Durden runs an 80-employee mom-and-pop injection molding shop in Auburn, Ga., but he has done something that few such shops have done - invest in an SLA 250 rapid prototyping machine. The $250,000 SLA machine is quite an addition for Durden Enterprises Inc., which runs just nine presses, with clamping forces of 25-300 tons.
``We're not doing [rapid prototyping] from the standpoint of rapid prototyped parts, but rapid tooling,'' Durden said. ``Our real reason for existence is that we do an awful lot of aluminum tooling designed to do production.''
Durden guarantees the aluminum mold for 100,000 parts, and it is primarily for small-run jobs, where product life is short.
``We began to realize that there are lots of processes out there that could help us reduce lead times and reduce costs,'' Durden said.
With the SLA 250, Durden makes a prototype part, then take the same computer-aided-design file to build a core and cavity master. He then sends the core and cavity master to Keltool Inc. in St. Paul, Minn., where the master is turned into an A-6 steel tool insert.
When Durden gets the insert back, he puts it into the mold plates and adds cooling lines. The entire process takes about six to eight weeks.
``The neat thing about it is, it becomes more cost-efficient the more complicated the part is,'' he said.
Terry Wohlers of Wohlers Associates in Fort Collins, Colo., said that for a long time the missing piece of the puzzle of how to build tooling quickly and cheaply was coming up with a fast way to produce patterns, or a master of the core and cavity. Stereolitho-graphy permits that, he said.
Wohlers said that at Keltool, ``They're getting as many as a million injection shots off the tool with turnaround times of four weeks, at average cost of $1,200 -and for a premium of $900 you can get it in seven days.''
Wayne Duescher is president of Keltool, whose primary customers are custom injection molders.
He said many of the management people who wanted a way to get products in the customers' hands quickly ``didn't have intimate knowledge of the work and effort involved in getting the accuracies'' of a part.''
``This frustrated people because they were told it would be two weeks, but ended up being more than that,'' Duescher said.
Keltool teams up with part designers, marketing people and the mold makers, who all work together on a project. Duescher said rapid prototyping allows things to be done with a part that ``you'd have trouble doing with a 5-axis milling machine.''
Keltool makes the sintered metal cores and cavities from the master model furnished by people like Durden. The toolmakers finish the mold.
``If you do it as a team it almost guarantees success,'' Duescher said.
The one drawback to the Keltool process is that it is oriented to smaller parts, 4 cubic inches per cavity, because the accuracy is better.
The bottom line, Durden said, is that ``in Atlanta, Lockheed has a [three-dimensional stereolithography] machine, Georgia Tech has a 3-D machine and Durden Enterprises has a 3-D machine. As a mom-and-pop shop, that gives me an edge over my competitors.''
