Vaakumlaua projekteerimine CNC freespingile

Lõputöö eesmärk oli projekteerida ettevõttele Merrem Tööstusplast OÜ ettevõtte siseseks kasutamiseks mõeldud freespingi vaakumlaud. Ettevõtte poolt oli esitatud lauale hulk nõudmisi, mis kõik said täidetud. Valminud laua tööpind on mõõtmetega, mis võimaldab ära kasutada kogu freespingi telgede liikumisulatuse. Laud on piisavalt jäik, et see ei painduks läbi ka suurima lubatud koormuse all. Vaakumtrassiga ühendamiseks ei ole vaja pinki ümber ehitada, ega liigselt modifitseerida. Projekteeritud vaakumiühendus ei jää segama freespingi tööd. Laua pealmisele osale sisse freesitud soonte abil on võimalik lauda jagada väiksemateks osadeks. Projekteerimise osas kirjeldati ja põhjendati erinevate lahenduste ning materjalide kasutamist. Selgitati, miks tehakse laud kahest osast, miks tehakse pealmine osa soontega ning kuidas toimub laua ülemise ja alumise poole omavaheline liitmine ja tihendamine. Selgitati vaakumiühenduse jaoks vajalike avade mõõtmete valikut. Tugevusanalüüsides arvutati välja lauale mõjuvate jõudude suurused. Uuriti lauas tekkivate sisepingete ja läbipainde suuruseid. Analüüsidest selgus, et kõik laua osad peavad tekkivatele pingetele ja koormustele vastu ning ettevõtte poolse kasutamise tulemusel ei ületa tulemused lubatud piire. Nii vaakumlaud kui ka vaakumiühendus valmistati ettevõttes kohapeal. Töötlemisel kasutati kahte freespinki. Lisaks teostati mõned operatsioonid käsitsi. Majanduslikus pooles käsitleti laua valmistamiseks kuluvat maksumust ja tasuvusaega. Kulu osas käistleti eraldi materjali maksumust ja koos tööjõu ning masina aegadele kuluvat maksumust. Tasuvusaja arvutamiseks kasutati ajaliselt mõõdetud Leiti, et laua hinnanguline tasuvusaeg on umbes 44 tööpäeva, ehk ligikaudu kaks kuud.

SUMMARY Increasing energy prices, labour costs, material prices, etc. are forcing companies to find ways to cut costs in order to stay competitive and increase profits. One of the possibilities is to review the production and make it more efficient. In general, production efficiency can be improved by reviewing the entire production process and, if necessary, making changes in technology. In addition, each process can be improved individually. In the case of CNC machining, this could be, for example, an improvement of the machining programs, by using different cutting tools that allow for greater cutting depths, higher feed rates, etc. In addition, time can be saved by clamping the workpieces on the workbench. By using special fixtures, it is possible to do this faster and more efficiently than using conventional machine tools. This is especially the case for more complex parts, which often cannot be machined on conventional machine tools. One way of clamping parts on a workbench is to use a vacuum. This method of clamping allows parts to be machined from both the top and the sides without the clamping elements interfering with the milling operation. The aim of this thesis was to design a vacuum table for clamping parts on a milling machine used in Merrem Tööstusplast. Compared to the current solution with machine rods, the use of a vacuum table allows to reduce the time required for changing parts. The efficiency of the bench itself is also increased, as several different parts can be machined in succession with one tool and only then the tool can be changed. In addition, the vacuum makes it easier to clamp parts of unusual shapes that would require special fixtures using other clamping methods. It is also an advantage when machining very thin or soft materials, which can deform excessively when using gouge bars. It is important for the company to meet its customers' expectations in terms of delivery times, quality and price, and to be able to offer all the parts from a single source, it is important that the company is able to produce such parts itself. By designing a vacuum table the company is acquiring the capability to do so. Therefore, the company would benefit from the vacuum table greatly. The company has a large and diversified customer base around the world, their orders include parts that would be most efficiently produced using a vacuum table. Until now, such orders have been outsourced. In some cases, it has not been possible to work with subcontractors to achieve a price that would satisfy the customer, and some work has had to be abandoned. The reason for the decision to use a vacuum table on the milling machine rather than a router is purely economic. The acquisition cost of a router capable of guaranteeing the same accuracy as a milling machine is expensive. The decision to manufacture the table itself is justified by the fact that there is no table available for purchase in the required dimensions to meet the conditions set by the company. As a result, the vacuum table was designed and all the requirements for the table set by the company were met. The company itself already has six three-axis milling machines, therefore one of the milling machines in use was adapted to a vacuum table. The chosen milling machine was a Doosan DNM6700. The decisive factor in the choice was that, as it is the newest milling machine, it has the longest expected service life. When designing the solution, it was also important to ensure that it was compatible with other standard products already in use in the company. The working surface of the completed table has dimensions that allow the full range of motion of the milling machine axes to be utilised. The table is rigid enough not to buckle even under the maximum allowable load. There is no need to rebuild the bench or modify it excessively in order to connect it to the vacuum line. The designed vacuum connection will not interfere with the operation of the milling machine. The grooves milled into the top of the table allow the table to be divided into smaller sections. In the design part, the use of different solutions and materials was described and justified. It was explained why the table is made in two parts, why the upper part is made with grooves and how the upper and lower parts of the table are joined and sealed. The choice of the dimensions of the openings required for the vacuum joint was explained. The FEM analyses were used to calculate the forces acting on the table. The magnitudes of internal stresses and deflection forces on the table were investigated. The analyses showed that all the parts of the table can withstand the stresses and loads generated and that the results do not exceed the permissible limits when used by the company. Both the vacuum table and the vacuum connection were manufactured in-house. Two milling machines were used for machining. In addition, some operations were carried out manually. On the economic feasibility, the cost and the payback time for the production of the table were considered. On the cost side, the cost of the material was considered separately, and together with the cost of the thrust and the machine time. To calculate the payback period, a time-measured payback period of about 44 working days, or two months, was estimated. Overall, the vacuum table was immediately put into operation in the company. After two weeks of operation, it can be said that, compared to the previous machine tool, set-up times for all products have been reduced by an average of 40%.