Efficient deburring with robots

ニュルティンゲンに本社を置くKADIA Produktion GmbH + Co.社の歴史は、1959年のホーニング工具の製造から始まりました。最初のホーニング盤は創業から10年後に開発されました。1981年同社はバリ取り機の製造と共に、別の事業分野に参入しました。現在、KADIA社はホーニングおよびバリ取り技術のリーディング・スペシャリストであり、200名の従業員を擁しています。

主な顧客は、自動車メーカーやサプライヤー、建設・農業機械メーカー、風力発電所メーカー、航空宇宙産業などです。同社は、ホーニング加工用にさまざまなサイズの標準機を提供してますが、バリ取り加工用には原則としてカスタムマシンを製造しています。顧客にはバリ取りのエキスパートとしてKADIA社を採用する大手機械メーカーも含まれています。

機械加工では、緩いバリと固定されたバリを区別します。バリ取りの後、要求されるものによって、部品はシャープなエッジ、エッジの丸み、または面取りが必要で、これがエッジデザインとも呼ばれる理由です。バリを評価するために、KADIA社はシャープペンシルの芯を5ミリ出して、簡単ですが大切なテストを行います。その芯でバリを取り除くことができれば、バリは緩んでいるといえます。芯が折れるようであれば、それは固定バリであり、削り取る必要があるか、後で外れることはないのでそのままにしておくことができます。

ロボットを使用する加工プロセスでは、ワークのサイズも重要です。ワークピースをガイドすることは、小さな部品に適しています。ロボットは固定された加工ユニットに沿ってワークをガイドします。ツールガイド方式では、ロボットアームがしっかりと固定されたワークを加工します。「大きなワークピースの場合、かさばるパーツを移動させるよりもフライスカッターを手に持って加工する方がはるかに巧みです。」とKADIAのデバリング＆ロボティクスのセールススペシャリスト、ヤニック・ヴァイス氏は説明します。

The centrepiece of development at KADIA is a five-by-six-metre test cell with a six-axle industrial robot and a quick-release unit. This enables testing of what is set to go on to become the system. Preliminary tests determine the optimum cutting data and assess stability. The cell is home to 15 changeable units. The robot has automated access with an action radius of 2.70 m to nine of these. Each unit represents a specific function that is used for machining a part. Typically, it consists of a motor spindle with a connection and a cutting tool.

A rotary table as the seventh axle is also part of the equipment of the test cell, which also has enough space to accommodate other systems, such as coolant supply or additional process units. At KADIA, several parts are equipped for various tests in the cell at the same time.

For initial preliminary tests on a dummy part for the battery tray, KADIA used a round-insert milling cutter already in stock in. The tool proved wholly unsuitable for the task. The vibrations that occurred were so severe that even the processing spindle was damaged. Even with low cutting values, the background noise during milling was still noticeable in the adjacent building.

With the task to deliver a suitable milling cutter for the aluminium housing, MAPAL was chosen as the partner of choice. “We evaluate in advance in which tool manufacturer we see the potential for cooperation,” says Jannik Weiss. Although KADIA initially focuses on standard tools, it was a major plus for MAPAL that the tool manufacturer produces custom tools where necessary.

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.