Now that the global economy is finally starting to put the financial crisis behind it, confidence is returning to many industrial sectors. The moldmaking industry is no exception—with this renewed confidence predicted to fuel a buying spree.
According to a survey conducted last year by Gardner Business Media, a U.S. publishing company, moldmaking companies expect to increase their spending on production equipment by over 30% this year compared to 2014, up to $500 million. This is nearly ten times the average amount they spent on equipment between 2008 and 2012.
So what are these moldmaking companies going to spend their $500 million on? As well as buying equipment in order to expand their production capacity, these companies also want to invest in advanced mold fabrication machines offering enhanced production efficiencies with reduced costs.
One way to achieve this is with state-of-the-art versions of existing fabrication techniques, such as computer numerical control (CNC) machining and electrical discharge machining (EDM). Another is with an entirely novel fabrication technique that’s just being introduced to moldmaking.
EDM Complements CNC
CNC machining and EDM still form the centerpiece of most moldmaking operations. They’re used to cut metallic materials such as steel, aluminum, and beryllium-copper alloy into defined shapes. CNC machining is the more conventional of the two techniques, using various different tools, including drills and rotary milling cutters, to remove material from metal via mechanical forces.
EDM, by contrast, removes material via electrical discharges between two electrodes, with the metal to be shaped acting as one of the electrodes, known as the workpiece. The other electrode, known as the tool, is usually made from graphite and can be moved in relation to the fixed workpiece. The two electrodes are separated by a dielectric liquid, usually some form of oil, with a voltage set up between them.
Because of the intervening dielectric liquid, current only flows between the electrodes when they are brought close enough together to overcome the dielectric, producing a spark that removes material from both electrodes. By moving the die-sink EDM tool (or metal wire electrode, as in wire EDM) and repeatedly bringing it close enough to the workpiece to induce an electrical discharge, this process can cut desired shapes into the metal.
Together, CNC machining and EDM can produce molds with complex shapes at high resolutions. CNC machining tends to be faster than EDM, but EDM can work with tough metals such as hardened steel that can be difficult to process using mechanical forces. EDM has also generally been able to etch smaller features than possible with CNC machining, on the scale of micrometers.
In both CNC machining and EDM, the specific shapes carved into the metal to produce the mold are defined by computer-aided design (CAD) and computer-aided manufacturing (CAM) software tools. In the latest machines, this is now being combined with robotics to reduce operator involvement as much as possible. Thus, the latest CNC machines can automatically switch tools, and the latest EDM machines can automatically switch different tool electrodes.
These latest machines can even be run “lights-out,” meaning without any operators being present, including overnight. The machines are monitored remotely, allowing the operators to be informed if the machines stop working or if there are any other problems, but otherwise they are simply left to get on with producing the mold.
Increasing the number of axes of movement in CNC machining has also helped with lights-out operation. Conventional CNC machines can move tools in three distinct directions: left and right, forward and backward, and up and down. The latest machines, such as the C 52 U from Hermle Machine Company, can also rotate the tools around one or two of these directions, providing them with a fourth and fifth axis of movement. This allows complex shapes to be cut into a piece of metal without having to move it around, saving time and reducing operator involvement.
When operator involvement is still required (such as to import CAD data into the machines or set up the jobs), it’s now usually done using a touchscreen and intuitive software, making the whole process as easy as possible. Removing human involvement as far as possible helps to increase production efficiency, as does increasing the cutting speed while reducing energy requirements. The latest moldmaking machines, such as the AL600 wire EDM system from Accutex Technologies Co., boast all these capabilities.
Tool Wear & Repair
Another way to enhance the production efficiency of EDM is by reducing the wear on the tool electrode. This can be done by altering the current shape of the electrical discharge to match cutting requirements. Known as adaptive current-shape technology, this is the approach being adopted by OPS Ingersoll in its new Gantry Eagle 500 die-sink EDM machines.
Wear is also clearly an issue for the tools used in CNC machining, but the approach for reducing this wear is rather more traditional: make tougher tools. Despite the long history of milling, drilling, and grinding tools, manufacturers are still finding ways to increase their toughness. For example, the German company Wexo Präzisionswerkzeuge GmbH has introduced a new range of advanced milling tools which contain a special cutting geometry and a nano-coating to reduce wear.
Despite all these increases in efficiency, molds are still very expensive to make. The high cost of molds, together with concerns about resource use, are leading to a growing interest in repairing damaged or worn-out molds.
Traditionally, this has been done using some form of arc welding, usually gas tungsten or plasma, but its precision is not high enough for molds containing very small features. It’s thus being superseded by laser welding, with the latest systems using high-power diode lasers to melt damaged areas of the mold and deposit new metal by melting a wire or metal powder. Laser welding is very precise, allowing the deposition of material in a thickness of tens of micrometers, and the latest systems are highly automated.
It’s only a small jump from laser welding to proper additive manufacturing, which is also beginning to be used to repair molds. More famously known as 3-D printing, this involves building up a computer-generated design, layer-by-layer. Similar to laser welding, laser sintering is done by depositing successive layers of metal powder, which is heated with a laser and then left to solidify. Alternatively, 3-D printing can be done by depositing layers of plastic that harden on cooling or on exposure to ultraviolet light.
Several companies, such as Ecoparts and Innomia, are now offering additive manufacturing as a means to repair metal molds. This usually involves removing the damaged section and then fabricating a replacement directly onto the mold with laser sintering. Replicating the damaged section can be done either by taking advantage of the CAD files used to produce the original mold or, when they’re not available, by using areas of the mold adjoining the damaged section as a template.
As well as for repairing molds, additive manufacturing also offers an entirely novel way to make molds—especially complex molds with tiny features. The U.S. 3-D printer manufacturer Stratasys is already marketing its Objet 3-D printer for use in making injection molds. These molds are produced from acrylonitrile butadiene styrene (ABS) rather than metal and so are only robust enough to act as prototype molds rather than for production. Able to withstand up to 100 injection-molding production cycles, they cost much less to produce than metal molds, allowing a design to be tested and tweaked multiple times.
The latest laser-sintering system makers also have moldmaking in their sights. Last year, the German additive manufacturing company EOS launched its EOS M 400 laser sintering system, which the company says can be used to produce metal molds. At the moment, these molds can only be produced from aluminum and a nickel alloy, but EOS says that it’s working on introducing other materials as well.
In addition, Japan’s Matsuura Machinery Corp. recently launched a laser sintering system specifically designed for moldmaking. Called the Lumex Avance-25, it combines laser sintering with high-speed milling technology, using laser sintering to fabricate complex shapes and milling to process their surfaces.
All this just in time for the forthcoming buying spree.