A Tour of the Metabo Power Tool Factory in Germany

This past June I was among a group of bloggers who were guests of Metabo on a trip to their factory in Germany. I’ve been to factories before, and what stands out about this one is the amount of production that is done in-house. No tool company produces 100% of the parts that go into its power tools, but Metabo claims to produce a far greater percentage than its competitors.

I asked about this and was told they outsource only those parts that can’t be produced in-house, or that can be produced more economically (but equally well) by others. This would include items such as cords, switches, electronics, bearings, and battery cells. But like any of the better tool companies, Metabo is intimately involved in the design of those components and rigorously checks their quality when they arrive at the plant.

Ours was the first tour group permitted to take photos and video inside the factory. A friend of mine had been there before, and he was not allowed to bring a camera. So unless you work for Metabo or have been on a tour of the plant, this will be your first opportunity to see what goes on inside.

For the sake of transparency, I’d like to remind you that media event hosts typically cover airfare, hotel, food, and in some cases entertainment. This trip was no different.

Our tour began with a presentation on the history and scope of the company. Metabo is headquartered in Nürtingen, which is just outside of Stuttgart. Its factory and office buildings cover roughly 15 acres of ground. I was not able to get far enough back for a good overall photo, so here’s an aerial shot from the company website. See Google Maps for a better view of the factory and surrounding area.

There are 1,080 employees at the Nürtingen facility, and another 620 at other locations around the world, including a plant in Shanghai, China.

In March 2016 the company was acquired by Hitachi, which earlier this year was sold to private equity firm KKR. It’s unclear what this will mean for the Metabo brand.

The company was founded in the 1920s as Schnizler GmbH; its first product was a hand-cranked drill known in German as a metallbohrdreher. By 1935 the company had changed its name and produced its first electric drill. The name Metabo is derived from metallbohrer (metal drill), which seems fitting given the company’s long association with metalworking tools.

The first thing we saw upon entering the factory was a series of old-school work benches, arranged like those in a high school shop or chemistry lab. Like most German manufacturers, Metabo has a training program for apprentices, who are trained in this area. They begin with basic bench skills, such as using metal files and measuring tools, and advance to operating mills, lathes, and CNC equipment.

An apprentice who completes the program is offered a job at the company. One of the people who showed us around the factory had been a Metabo apprentice 25 years before.

Rotors, Motors, and Gears

Metal comes into the factory as steel bar stock and aluminum ingots. The steel bars shown here will be loaded into the CNC machine on the right.

These grinder arbors were milled in a CNC machine. They are evenly spaced apart in steel bins so they can be sent through a furnace for heat treating.

The chips and shavings removed by machining fall into bins at the ends of the CNC equipment. The waste from parts machined without cutting oil is clean enough to go directly to a recycler. If the waste contains oil it must be cleaned before recycling, and Metabo does this by running it through some kind of “washing” machine.

Steel parts are typically machined before the metal is heat-treated, a process that hardens the surface while leaving a resilient core. The gray surface of the gears above indicates they have undergone heat-treating.

The gears shown here are only partially machined and will undergo a second light machining to bring them to final dimension. The final machining will also give the gears a shiny finish.

Steel parts are hardened by heating them in a furnace and then cooling them in a highly controlled manner. These gas-fired furnaces can reach a temperature of 1700°F, and can heat up to 550 pounds of parts at a time.

These motor shafts were perfectly straight when machined but may have become slightly distorted by the heat treatment process that followed.

If a motor shaft isn’t perfectly straight, the rotor (the spinning part of the motor) will wobble. To prevent this from happening, shafts are run through a machine that inspects them for straightness, and when necessary bends them back to within spec. This is done to every shaft in every motor produced at the factory.

It’s common for tool companies to wind their own motors—I’ve seen it done in a number of factories. The process begins with the installation of the armature stack (a series of identical steel stampings) over an insulating material pressed onto the shaft.

The copper wire must be electrically isolated from the armature stack. This is done by covering the ends of the stack with a cardboard-like insulation material (the tan stuff) and inserting a similar material (the green stuff) in the slots that will house the wire.

Metabo uses different diameter wire for different types of motor. Each of these kegs contains 100 kilos (220 pounds) of copper wire.

The machine that winds rotors moves in an incomprehensible blur of motion. It reminded me of a sewing machine, in the sense that a thin strand of material (copper wire) is fed through a series of tensioning rollers before being manipulated to create the desired effect.

A similar method is used to wind the stator, the stationary coil that surrounds the rotor in the assembled motor. We were not allowed to photograph that part of the process because there is something super-secret about the way it is done in Metabo’s new “low profile” stators.

After the rotor is wound, insulation material is inserted into the slots to cover the top of the wire. Next, the gaps between the copper wire are filled with epoxy, to make it easier for the motor to disperse heat and reduce the likelihood of electrical shorting. Metabo does this by subjecting the rotor to a powder coating process that deposits powdered epoxy on the copper parts only. The rotor is then sent through an oven that bakes the epoxy into a solid mass.

Stuart’s Note: If you have ever pushed a tool to where smoke comes out of it, that’s usually the motor windings getting so hot that the epoxy starts to burn off.

The rotors above have been powder coated with two different colors of epoxy, green at one end and red at the other.

When the rotors have cooled an automatic machine sands excess epoxy from the armature stack and commutator bars.

Next, rotors are balanced by spinning them in a machine that senses where they are heavy and removes weight by shaving away parts of the armature stack.

These rotors are being checked for balance after the installation of the plastic cooling fans.

The final stop is a testing machine that runs 5,000 volts through each rotor. If the rotor passes it goes on to the assembly area; if it fails, it goes in the trash. Stators undergo similar testing.

Among the more impressive things we saw was the die-casting of aluminum parts, such as gear housings and guards.

Die-Casting and Injection Molding

Aluminum enters the factory as ingots.

Ingots are melted in a gas-fueled furnace at 1650°F, and the liquid metal is poured into crucibles and transported to the die-casting machines.

The furnace runs year-round, because it takes less energy to keep the 10-12 tons of aluminum it contains in a liquid state, than to re-melt it all after a holiday shutdown.

Heavy steel dies (like the ones above) are inserted into the die-casting machine, which forms parts by ramming molten aluminum into the hollow areas within the dies.

After the metal solidifies the dies split open and the parts drop out.

Parts such as these gear housings for grinders are typically cast in multiples. Molten aluminum enters the die at the “sprue” and passes through “runners” on its way to the parts. The material that hardens in these channels does not go to waste; it’s broken free from the parts and sent back to the furnace for re-melting.

Most of the plastic parts in a Metabo tool are produced in-house using injection molding machines.

This would include motor housings, handles, and the battery casings shown here.

Plastic parts begin as small plastic chips that are sucked into a vacuum hose and fed into injection molding machines.

The plastic melts in the machine and is forced into dies. After the plastic solidifies, the dies are opened and the newly formed parts fall or are pushed out. Dies can be swapped in and out of machines; this one is currently making motor housing components.

These are parts of the dies used to make tool handles.

Here is just a single aisle in an area filled with rack after rack of dies for plastic injection molding and aluminum die-casting. I was told Metabo has 34 million Euros (38.3 million USD) tied up in dies.

This is the back side of the work stations in an assembly cell. Parts are stocked from the rear so the people assembling tools do not run out. I did not photograph the front because we were not allowed to photograph workers without their permission.

Performance Testing

Like almost every tool company, Metabo tests products to make sure they perform as designed. The cordless grinder above has been placed in a dust testing chamber, where it will be run for a long period of time while being blasted by thick clouds of dust.

This is a corded grinder after dust testing. The idea is to see what happens to tools when they are exposed to concrete dust, metal filings, and other substances that can damage internal parts such as windings and bearings. Metabo will redesign certain components if excessive wear is detected. For example, the company now puts a sort of “shield” on cooling fans in grinders—to deflect airborne debris and prevent it from abrading motor windings.

Metabo tests tools in number of ways. In the first two parts of the video above, motors are being testing by connecting assembled tools to dynamometers and running them through a program of varying speed and torque while data is logged on computers. In the last two parts of the video, the hammer function is being tested by running them against a steel fixture. I’ve seen similar setups in development labs at several other tool companies.

I can’t tell you who makes the red tool, but the planers and grinder are from Hitachi, which bought Metabo in 2016. All are being tested with some kind of dynamometer.

These shelves outside the test lab contain tools made by competitors. Like most other companies, Metabo tests competitors’ tools to see how theirs stack up. It would be unusual to go to a tool company development and testing lab and NOT see competing brands of tools.

Not all testing is performed in the lab; in a separate testing area humans and robots test tools in more real-world manner. This fellow is testing a cordless grinder by cutting piece after piece of angle iron.

In another test, workers drill hole after hole in concrete. The dumpsters outside of this building are filled concrete debris from testing. I was told drilling and chipping tests produce 20 tons of concrete dust per year.

I hope you enjoyed this look at some of what happens at Metabo’s factory and HQ in Germany. At the end of the tour they took us to the training area and showed us some of the tools produced at the plant. I was familiar with many of them, though there were also some prototypes of tools that are currently under development. In the coming weeks I’ll do follow-up pieces on some of the more interesting new tools they showed us.