Efficient deburring with robots

The story of Nürtingen-based KADIA Produktion GmbH + Co began back in 1959 with the production of honing tools. The first honing machines were developed ten years later. The company tapped into another branch of business in 1981 with the manufacture of deburring machines. Today, KADIA is a leading specialist in honing and deburring technology and currently employs 200 people.

Its main customers are car manufacturers and suppliers, construction and agricultural machinery manufacturers, wind power plant producers and the aerospace industry. While the manufacturer offers standard machinery in different sizes for honing, in principle, custom machines are built for deburring. Customers include major machine manufacturers that bring KADIA on board as a deburring expert.

In mechanical machining, a distinction is made between loose and fixed burrs. After deburring, depending on what’s required, the part should have sharp edges, edge rounding or a chamfer, which is why this is also known as edge design. To assess a burr, KADIA uses a simple but meaningful test using the lead of a mechanical pencil extended by five millimetres. If it can be used to remove the burr, then the burr is loose. If the lead breaks, it’s a fixed burr, which needs to either be milled off or can be left in place, as it won’t come off later.

The size of the workpiece is also crucial to machining processes that make use of robots. Guiding the workpiece is favoured for smaller parts. The robot guides the workpiece along fixed processing units. In a tool-guided strategy, the robot arm processes a workpiece firmly clamped in place. “For bigger workpieces, I’m much more skilful with the milling cutter in hand than if I have to move the bulky part,” explains Jannik Weiss, Sales Specialist Deburring & Robotics at KADIA.

KADIA社の開発の中心は、6軸産業用ロボットとクイック・リリース・ユニットを備えた5×6メートルのテストセルです。これにより、システムになる予定のものをテストすることが可能です。予備テストでは最適な切断データを決定し、安定性を評価します。セルには15個の交換可能なユニットがあり、ロボットは、このうち9つのユニットに半径2.70mで自動アクセスすることができます。各ユニットは、部品の加工に使用される特定の機能を表しています。一般的には、接続部と切削工具を備えたモータースピンドルで構成されています。

7軸目となる回転テーブルもテストセルの設備の一部であり、クーラント供給や追加プロセスユニットなど、他のシステムを収容する十分なスペースもあります。KADIA社では、同時にセル内で様々なテストを行うために複数の部品を装備しています。

バッテリー・トレイ用のダミー部品の初期予備テストでは、KADIA社はすでに在庫していたラウンド・インサート・ミーリング・カッターを使用しました。しかしこの工具は、この作業には全く適さないことが判明しました。発生した振動は非常に激しく、加工スピンドルさえも損傷したのです。切削値が低くてもフライス加工中のバックグラウンドノイズは隣接する建物にも響いていました。

アルミニウム製ハウジングに適したフライスカッターを提供するという課題において、MAPAL社がパートナーとして選ばれました。「私たちはどの工具メーカーとの協力が可能かを事前に評価しています。」とヤニック・ヴァイス氏は言います。KADIA社は当初、標準工具に重点を置いていました。工具メーカーが必要に応じてカスタム工具を製造することは、MAPAL社にとって大きなプラスでした。

But Norbert Meier, who wanted to show the customer an alternative with the second milling cutter, had reckoned with this outcome. “We specially developed our FlyCutter for requirements like these,” he explains. MAPAL developed the lightweight tool specifically for unstable machining requirements that occur in robot applications. It is optimised for small connections such as BT30. The innovative design and use of aluminium ensure the milling head is particularly lightweight. With the diameter of 63 millimetres used at KADIA, the PCD milling head, including milling inserts, weighs just 220 grams.

The sensitive wedge adjustment make µ-precise adjustment of the milling inserts possible. The dovetail guide and an additional worm screw ensure perfect seating and high accuracy of repetition for the assembly of the milling inserts. The special, ultra-positive cutting edge geometry means only weak forces are applied to the part and the tool spindle guided by the robot.

When machining the battery tray, accuracy down to the µm is not required. In fact, to ensure the sealant applied by the automotive manufacturer holds better, a certain rawness of the surface is needed. Only the waviness must not be too high. In the tests, the milling cutter was moved beyond the limit to determine up to which point chatter marks on the relatively thin part still lay within the required tolerance.

“The crux of robot processing is the interplay between tool, fixture and robot,” explains Norbert Meier. Rigidity is a fundamental issue in machining. The further the robot arm extends, the more unstable the machining. That’s why KADIA doesn’t just test various cutting data, but also various positions for the robot, in front of or beside the workpiece.

In this case, the partners determined that the optimum cutting data for a spindle speed of 11,000 rpm was a feed of 0.16 m/s and material removal rate of 0.5 mm. The FlyCutter reliably delivered very good surface quality. KADIA incorporated this test data into the concept for the custom machine. The manufacturer therefore determined that the use of three robots in one cell would be the most cost-efficient solution for series production. While two share machining on the front side, the third works on the rear. In addition to the cutting data, KADIA delivers the customer with the duration of the machining steps and the cycle time that can be achieved. Accordingly, deburring a large battery tray will take around 80 seconds. “In a robot process, such process information on cutting data is not as standard as for a CNC machine. Depending on the robot’s positioning, the same data generates different results,” says Jannik Weiss.

Due to the thoroughly positive results, KADIA and MAPAL wish to deepen their cooperation. Further testing for various machining processes is already planned.