Development of the automatic machine for tube end forming

Transcription

1 Development of the automatic machine for tube end forming Matjaž Sotler, machine manufacturing TPV d.d. ABSTRACT In this article I tried to demonstrate how company TPV d.d. progresses from stage of demand by the contractor to the final product, with the use of modern engineering approach. This study shows the methodology of solving a problem, starting from breakdown of a main challenge into few smaller problems, to finding solutions for these breakdown problems. I used s modern software to simulate processes of the forming of the tube. To do that, first I had to calculate forces needed for the deformation, which were the input data for the virtual simulation. The final product is a cold tube forming machine which started as an idea, and went to be a product I am presenting today. Company introduction Company TPV d.d. is a well-recognized development supplier in the automotive industry. We produce car seats as a whole and also components for those car seats. We also produce car body chassis components, engine gaskets, etc. We are a development supplier for big car brands like BMW, Daimler, Renault, Nissan and many others. TPV Avto is a company for marketing and maintenance of vehicles, and is the biggest passenger cars dealer in the region of Dolenjska and one of the biggest dealers on the national level. Our company also produces car trailers. Besides the parent company TPV d.d., the TPV Group consists of four other companies TPV Prikolice, TPV Avto, TPV Center and TPV Šumadija. Working hand in hand Company cooperates with Šolski center Novo Mesto for a few years now and we offer support to the local school system by giving students a chance to finish their mandatory practice in our company with mentor being assigned to each student. Many of our employees got their education in this school center. Project introduction The company got an order from its contractor and immediately after, a team of experts were assigned to the project. Demands for the special purpose device were defined by this team of experts. Product intended to be produced on this device, is a tube with its diameter of 12 mm with the wall thickness of 1.5 mm. Material used for this part is steel S355 with its yield strength of 325 Mpa according to Krautov engineering manual. Additional specifications from the contractor are that the device must be able to process tubes made from high strength steels and has to have diameters up to 18 mm and a maximum wall thickness of 2 mm. Yield strength of this steel is much greater, roughly around Rm=700 to

2 900 MPa. The contractor s specification on the machine cycle was 17 s but we concluded that the machine cycle must not reach more than 13 s, due to the possible machine jamming and probable bad parts. This way we can assure a stable production process. Theory At the very beginning of the construction process we had to make a mathematical model which was needed to calculate the forces needed to make the component. We used plain and simple equation of Hooks law which we applied to different diameters of tubes with different wall thickness and different yield strengths. This calculation was done just to get an approximate data of the value of the needed force. This would be tested later on with the real tube in the production, on a similar device. Table : Forces needed for deforming Number Tube diameter [mm] wall thickness [mm] 1,5 2 1,5 2 1,5 2 1,5 2 Yield strength[mpa] Force [kn] 25,27 32,67 43,54 56,30 16,08 20,42 27,71 35,19 With known forces, we could test forming of the tube in a digital environment with software CATIA and its FMA module. The analysis gave me an approximate view of the internal stress of the material while being formed. Market and production process analysis Picture : Tube folding with FMA One of the first steps in designing and defining the device is analysis of market and the devices that are already in the production processes. Company already owns few forming

3 solutions like linear tube forging, rotary forging better known as swaging and electrical forging which was abandoned in the following processes due to economic reasons. One of the demands from our contractor was that the device must operate on its own for at least 30 minutes, which meant that the process itself must be automated and device has to have a storage bunker for the input material as well as a crate for the finished parts. Part of the study was also technologies of the input bunkers, where we recognized different solutions for storage and transferring tubes forward through the process. One solution had the tubes fall out of the bunker with the help of gravity, while we needed some sort of an actuator for blocking and unblocking the tube with the falling control device. Second solution had the tubes transferred from the bunker with the help of chains connected to a motor. Third solution had the ramp moving up and down the bunker, where the ramp was angled so that the tubes rolled by themselves to the ramp (picture 3 in the chapter Modeled machine and basic movements ). Actuator raised and lowered the ramp in three stages and that assured that only one tube reached the highest bed place for the tube. At this point a prototype tool was made in the workshop and then tested on a similar device in our production process. Existing device had a pressure regulator and a manometer which allowed us to determine at which pressure we achieve actual yield strength of the material. Now we had pressure and known dimensions of the cylinder and we could determine actual force needed for deformation. Solution analysis and evaluation All of the analyses were evaluated with numbers 1, 3 and 5 with 1 being the lowest and 5 being the highest rank. All results were entered in a table from which we would recognize the best possible solution. Result of this table would be a foundation for making the morphological matrix.

4 Table : Morphological matrix Feeder of input material Gravity-free fall Chain Console Tube positioner Air STOP M anually Servo positioning Clamping Hydraulic Air Electromechanics Forming Hydraulic Air Electromechanics Output slide Transfer Gravity-free fall Robot Concept Morphological matrix is the basis of making a concept on a paper. After the concept was drawn on the sheet of paper, the project team reviewed it and approved the concept upon which 3D modeling would begin and later on 2D documentation could be made.

5 0,3 0,5 0,8 1,0 1,3 1,5 1,8 2,0 2,3 2,5 2,8 3,0 3,3 3,5 3,8 4,0 4,3 4,5 4,8 5,0 5,3 5,5 5,8 6,0 6,3 6,5 6,8 7,0 7,3 7,5 7,8 8,0 8,3 8,5 8,8 9,0 9,3 9,5 9,8 10,0 10,3 10,5 10,8 11,0 11,3 11,5 11,8 12,0 12,3 12,5 12,8 13,0 Evaluation showed that the most appropriate technology for our application is the linear forming. Cycle of the machine was placed with an upper limit of 13 s so there was no other choice than to have an automated feeding of the tubes. Main demand of our contractor was that the operator only intervenes when he is filling the bunker with the input material. For the feeding of the tubes we found that the most suitable technology is solution number three mentioned previously in the text (Market and production process analysis). Prototype tool and testing of it on a similar device gave us the information we needed (forces, pressures and the time frames) in which we can make the parts. These time frames allowed us to make a machine cycle diagram on every operation of the machine in accordance with the concept drawn on a paper. Each operation was evaluated on how much time it would take to start and finish, so these values were entered in the table. Table : Machine cycle diagram Cy cle Time cycle Nu m. Operation Out In 1 Feeder out Feeder in Tube blockade out Tube push out Hy draulic clam p out Tube push in Tube blockade in Optim al clam p pressure+ + 9 Form ing out Optim al clam p pressure+ 11 Form ing in Hy draulic clam p in Push-out cy linder out Push-out cy linder in Laser on the output Feeder out-up End Cy lce Pot korak Diagram 3 Tube blockade out Tube push out Hy draulic clam p out Optim al clam p pressure Form ing out Push-out cy linder out Laser on the output + 1 End Cy lce Table is the base foundation for the designing of all the next stages down to the last drawing. Now we can continue with 3D modeling of the machine. Definition of hydraulic components With known forces needed for our application, I picked up a standard hydraulic cylinders from our supplier MAPRO. In the combination with the table of time cycles, I could calculate the flow of the pump and the power of the motor which would run the pump.

6 For defining the hydraulic pump we have to know volumes of all the hydraulic cylinders and the time periods to achieve each movement which tells us how much oil we need, to push the cylinder forward and backwards in a certain time frame. All flows and time periods were entered into a table. At this point we have to mention that the force of the cylinder and its volume is lower at the returning movement because the surface on which the pressure is applied is smaller, due to the diameter of the rod. Clamping cylinder Table : Flows of the clamping hydraulic cylinder Movement Volume [L] Time [s] Flow [L/min] Out 0, ,3 14, In 0, ,9 14, Forming cylinder Table : Flows of the forming hydraulic cylinder Movement Volume [L] Time [s] Flow [L/min] Out 0, ,1 17, In 0, ,5 16, The highest value of the flow is at the working movement of main cylinder and its value in theory is roughly 17.3 L/min. This value was used to calculate the power needed to achieve certain flow (17, 3) at the specific pressure (160 bar). Calculated value of the power needed for our application was 4.61 kw. We had to take into consideration account losses, due to friction and heat. Also, to be on the safe side, we used a standard electric motor with 5.5 Kw of power. Definition of air components For achieving needed movements of the parts in the machine we decided to use air cylinders, which are in comparasement with hydraulic or electric actuators in a severely lower price range. For the movement of tubes from the bunker to the defined position suitable for engaging hydraulic components, we used pneumatic cylinders from the local supplier SMC. Cylinders task was to move and separate each tube from a pile and transport it to the end position. Each movement and the position of the rod had to be checked by sensors and the control unit. If each of the components stopped before they reached end position for any reason, the machine would stop and enter safe mode.

7 Modeled machine and basic movements Picture 2: 3D Modeled device Picture 3: Angled ramp of the input feeder For these steps we had all the data we needed to finish up our modelling of the device. All of the hydraulic and pneumatic components were previously defined. All components exposed to

8 great forces and frictions were checked and calculated with the CATIA softer and its FMA module. Before step one and step two are engaged, pneumatic cylinder raises the tubes from bunker, which we can see in the picture 2 on the left side of the device. The bunker has a window covered with plexiglass plate so we can see what is going on inside. Step one is the moving mechanical blockade which comes to its final position at the angle 45 degrees on the central axis of our tube. In step two, pneumatic cylinder pushes the tube in to the matrix to its final mechanical blockade which was previously engaged. This step is crucial for the definition of the fold. That s why we made this mechanical blockade adjustable plus minus 3 mm in the axial translation of the tube. When adjustable blockade is set at the maximum plus 3 mm, the diameter of the fold on the tube is the smallest and vice versa if it is set at its minimum, minus 3 mm, the fold we get on the tube is the biggest. This is adjustable mechanically by the machine operator and when the device is in its safe mode. While the cylinder mentioned in step two is pushing the tube to the blockade, we engage first hydraulic cylinder marked as step three in the picture 2. This cylinder produces clamping force on the tube. Hydraulic system is designed with a pressure switch and if the pressure of the clamping device is insufficient we cannot engage the main forming cylinder. When we have met all of the mentioned conditions, control unit first removes the mechanical blockade mentioned in the step one and then removes the pneumatic cylinder from step two, which allows us to engage the main forming hydraulic cylinder marked as step 4. After the cold forming is made in step four, the hydraulic cylinder moves to its starting position, then the clamping cylinder moves to its starting position and the finished part is pushed by pneumatic cylinder, from the matrix. Finished part then drops by its own weight to the crate designated for finished parts. To be sure that the final component did really leave the matrix that holds it in while forming process are taking place, we installed a laser beam above the crate designated for finished parts. This prevents possible mechanical breaking of the device due to possible jamming of formed tube in the matrix. Safety Safe mode is achieved either by pushing the stop button on the device or by opening the safety cage to reach the mechanical components of the forming tool. Conclusion Data available to us at the beginning of the defining process was not sufficient. Only information we had at this point was the demanded time cycle, which was 17 s, along with parts that machine must process and the target price given from the commercial department of the company. As mentioned previously in the text, team decided to reduce the time cycle from 17 s, down to 13 s, to assure stable process. Explanation for this reduction is very simple, if we had a 17 s

9 cycle not only that the costs of one unit increases, but also we couldn t afford to have any machine downtime or replacement of bad parts. When we had information about the parts and the mechanical properties we calculated theoretical forces for the forming. The greatest force was recognized at the maximum diameter of 18 mm, wall thickness of 2 mm and mechanical properties of high strength steel with yield strength of Rp02 = 560 MPa, F = 56.3 Kn. With finite method analysis via software CATIA ; in virtual environment, we put it to the test and saw the stresses in the material while being formed. After review of the market and machines in the production process, we broke down the main problem to many smaller problems and compared this small problems with solutions from the review. These problems and few possible solutions were entered in a table and that is how we got a morphological matrix. This matrix was the basis from which we could make a concept following construction of the device. At this phase of making a concept, there were few ideas and few different approaches. Again, we reviewed and evaluated all concepts, made a table and recognized which of the solutions had the highest review value. At this point we could begin modeling the device with constant reviewing and constant risk assessment which assures safety of the future device. Later on, after the 3D models were created, we have made 2D documentation which we sent to tool shops around the country to get the best possible deals to make the parts. All hazard zones recognized within risk assessment were dealt with suitable safe guards. Automotive industry in which our company operates is highly demanding and it takes a lot of knowledge, experiences and innovative solutions to keep our share on the market. Automation, innovation and quality management are the motors of our company. Connecting innovative solutions is our vision. Device, described in the text above is one of many that the company intends to develop. This device will expand our share of the cold forming market and hopefully bring new employment opportunities. Contribution of this article is a procedure, explained in steps on how to start from the first document that comes from the contractor, down to the final product of the design team and finished 2D documentation. After 2 D documentation was made, offers were obtained from the tool shops around the country, the parts were made and assembled in the company. Assembled device was then equipped with electronic components and later on programmed and run by our electric department.