TPT November 2017

WE LD I NG

Tube clamping during machining operations TUBE machining operations present several technical challenges. The clamping and the behaviour of the tube during machining are two factors to consider. pins that are in contact with the tube when clamping. The adjustment of the elbow mandrel takes more time than a standard clamping system. However, it assures accuracy in the weld prep and can be used directly on-site.

Several parameters need to be taken into account to determine the most appropriate clamping system: diameter and wall thickness of the tube, access to the tube, requested machining accuracy, production rate, material of the tube and the possible contamination of the ID of the tube (for example, when machining tubes for the high purity industry). This is even more significant for on- site machining – the constraints become more stringent as the machine has to be portable. The clamping system must often support the cutting efforts and the weight of the machine while being as light as possible. Protem’s engineers paid attention to this issue to propose solutions for all industries and applications. Each clamping system was designed for a specific purpose. Inside clamping system: clamping by means of expansion blades is the most common system used to mount a machine inside the tube. It includes a shaft that is positioned inside the tube. The expansion blades are expanded when clamping the machine. Once the blades are in contact with the tube, the machine is clamped into the tube. The advantage of this system is the quick set-up and the range of diameters that can be covered. The machine will centre automatically into the tube without additional adjustment. Tubes can be machined one after the other very quickly, while obtaining a repetitive quality. Extra blades can be added to the basic expansion blades to reach larger diameters with the same machine. This does not affect the stability of the machine as long as the diameter remains within the range of diameters specified by the manufacturer. Greater contact between the tube and the expansion blades creates better rigidity and machining accuracy. Elbow mandrel assembly: elbow machining is a difficult operation that requires a specific clamping device. It is not possible to use a standard blade clamping system because of the elbow curve. The solution is to replace the expansion blades with contact

Inside collet clamping: clamping by use of an inside collet clamps machining units in small diameter tubes. The expansion blade system takes toomuch space when the ID of a tube is under 15mm (0.6"). The collet clamping system achieves contact on the entire circumference of the tube, avoiding deformation of thin-walled tubes when clamping the machine. The collet system is usually used on small machines that can be used in limited access areas and is perfectly adapted to small diameters and thin- walled tubes. One collet is necessary per diameter. Spider-type clamping system: this allows for a very precise adjustment of the concentricity and perpendicularity of the machine. The system has several arms that can be adjusted independently. This compensates for ovality defects and accurately centres the machine on tubes of large diameters. This device ensures stability and high accuracy machining. Outside clamping system: an outside collet clamping system is used to avoid contamination of the inside of the tubes while machining. This is critical for tubes used for network construction in the food, pharmaceutical, high purity or aerospace industries. Most of the tubes used in the high purity industry are manufactured with stainless steel. The collets are also made of stainless steel in order to avoid pollution. The use of a collet in contact with the entire circumference of the tube avoids tube deformation. When welding two tubes, their edges must be in perfect contact. Automatic orbital welding is the most used process in this type of industry and the welding preparation must be perfect to guarantee a good weld. The slightest deformation could compromise the welding operation. The choice of the right clamping system is essential. Outside clamping jaws: the clamping force can be very high to machine heavy-walled tubes or hard materials without risk of tube movement. In some cases, the machine is fixed on the tube with these types of jaws, allowing the tube to be cut directly on-site. OD

Prismatic clamping system

Outside clamping system

clamping allows for simultaneous cutting and bevelling. Unlike other types of clamping, the jaws cover a large range of diameters without changing parts and consequently meet industrial productivity constraints. Clamping with outside enveloping jaws: the enveloping jaws clamp on the exterior of the tube. The collets are mainly used on thin-walled tubes, while the enveloping jaws are considered for large diameter tubes. They are adapted for serial machining when they are installed on machines with high production capacity. Prismatic clamping system: this is made up of two jaws that come around the tube toward each other in four spots per set of jaws. This creates powerful clamping on the tubes, but can also cover a large range of diameters. It is used to achieve high production rates on different tube diameters and is powerful enough for heavy-walled tubes. The question of tube clamping can at first be considered minor. However, it is necessary to take all the parameters into account in order to perform perfect machining. Machining performed with an unsuitable clamping system can create damage to the tube and can jeopardise machining operations.

Protem SAS – France Website: www.protem.fr

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NOVEMBER 2017