At the exploitation of dies the defections that occur, due mainly to non operating rules of exploration, the improperly conditions of the machine (press) in terms of cinematic precision and the wearing elements in relative motion (ram displacement, wearing guides, etc) as the incorrect mounting of dies on the press. When installing dies must consider several aspects. Among the techniques used, especially for restoring the active elements in the work area are rectified frontal surfaces, hard chromating, hardening with electric sparks and charging welding. Were restored active profile and size of the work active elements so after reconditioning they corresponded in terms of dimensional precision and resistance to wear, like initial element

Alin STĂNCIOIU

Florin-Cristian CIOFU

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  Fiabilitate si Durabilitate - Fiability & Durability    Supplement no 1/ 2012   Editura “Academica Brâncuşi” , Târgu Jiu, ISSN 1844 – 640X     212 RESEARCH ON INCREASING ACTIVE LIFE OF CUTTING TOOLS  Alin STĂNCIOIU, University Constantin Brancuși, Targu-Jiu Florin-Cristian CIOFU, University Constantin Brancuși, Targu-Jiu  Abstract: At the exploitation of dies the defections that occur, due mainly to non operating rules of exploration, the improperly conditions of the machine (press) in terms of cinematic precision and the wearing elements in relative motion (ram displacement, wearing guides, etc) as the incorrect mounting of dies on the press. When installing dies must consider several aspects.  Among the techniques used, especially for restoring the active elements in the work area are rectified frontal surfaces, hard chromating, hardening with electric sparks and charging welding. Were restored active profile and size of the work active elements so after reconditioning they corresponded in terms of dimensional precision and resistance to wear, like initial elements.  Keywords: cutting, rectified, chromating,  sparks, charging, welding.   1.  The dies defections and remediation methods.  The wear active edges of dies depends on following factors: chemical composition and quality of the active elements of the dies; cutting edge hardness, nature and conditions of application of heat treatment, manufacturing process and the precision execution of active elements, cutting edge forms, methods of greasing and lubrication, stiffness components of dies and on assembly, semi - product cutting scheme, physico-mechanical properties of the workpiece and the kind treatment applied to this, workpiece thickness, cutting speed, etc. Also, the incorrectly calculated gaps can lead to the early galling and burr formation.     At the exploitation of dies the defections that occur, due mainly to non operating rules of  exploration,  the  improperly  conditions  of  the  machine  (press)  in  terms  of  cinematic precision and the wearing elements in relative motion (ram displacement, wearing guides, etc) as the incorrect mounting of dies on the press. When installing dies must consider several aspects. In the table 1 are represented the main types of defections that can occur during dies and molds exploration, as the methods that remedy them.       Table 1 Nr.crt  Type of defection  Cause  The  method  of remedy 1  Rapid blunting edges during cutting.          Inadequate heat treatment. Processing  by  correcting inadequate active edges. The  failure  of  the  functional gap  between  the  active elements.  Hardening by electric sparks. Executing  a  new review  of  the  active elements. Adjusting  the  cutting edge  of  the  active elements.   Fiabilitate si Durabilitate - Fiability & Durability    Supplement no 1/ 2012   Editura “Academica Brâncuşi” , Târgu Jiu, ISSN 1844 – 640X     213 2  Rapid blunting active edges on holes perforation.  3  Touching punch 1 of cutting edge 2.   Wrong mounting of the active elements. The press guide wear.  Waste  entering  or  two  semi-products between the working surfaces of dies. Fixing  and  correct centering  of  the  nail 3. Adjusting  the  press gap.  Using the elements of leading  of  the  semi-products. 4  Crumbled cutting edge.          The wear of the guide bushing or  columns  because inadequate heat tratament. Penetration of metal waste. The  voidness  bevels  which should follow the dies work. Replacing  columns and guide bushings. Welding  load  of chopped cutting edge.   5     The puncher cracked.  The dies hole 1 is coged with waste 2. The  heat  treatment  of  the matrix  was  made inadequately. Replace the matrix. 6  When  the  holes  are  drilling  it´s formed burr on the semi-product.   Large gaps between the punch and the active plaque.  Should  adjust  the gaps  between  the active elements. The cutting edges are corrected. 7  Disunite(dipress) the bushing guide 2 in the end plaque or the guide column 1 in motherboard.      Scratches  on  the  active surfaces by entering wastes. Replace  bush  guide or column. The  scratches  (small insignificant)  are removed  by  manual rectification(abrasive paste).     Fiabilitate si Durabilitate - Fiability & Durability    Supplement no 1/ 2012   Editura “Academica Brâncuşi” , Târgu Jiu, ISSN 1844 – 640X     214 8  Burrs at the die piece 1 to the cutting operation.    The  gap  between  the  punch and die is high. The active elements of cutting had moved. Adjusting the gaps or fixed the nail 3. Cutting  surfaces  are corrected. 9  The cut piece 2 is obtained concave or convex.  The active edge of the punch 1 and  the  extractor  3  aren´t adjusted. Adjusting  the  front active surfaces of the punch  and  the extractor  (after  spots of paint). 10  The punch of drilling 1 has cracked.  The  hole  dies  is  coged  with wastes 2. It should be replaced the punch. Should check the size and  the  form  of  the bore deviation. 11  The  blunting  active  edge  of  the punch.   The  thermal  treatment applicated  to  the  punch  is inadequate.   The  lack  of  lubrication elements in relative move. Replace punch. Adjusting gaps. Proper lubrication.  12   Bending punch.   The  heat  treatment  is inadequate.  Replace the punch.  Figures 1, 2 presents the images of the used tools viewed from the side and front with enlarged details at 6X for tools options investigated.                                      Fig.1  Improved punch OSC10                Fig.2 Improved edge punch – 6X      OSC10    Fiabilitate si Durabilitate - Fiability & Durability    Supplement no 1/ 2012   Editura “Academica Brâncuşi” , Târgu Jiu, ISSN 1844 – 640X     215       2. Preliminary operations for reconditioning of the active tools.       The  cutting  tools  that  were  used  were  removed  from  the  devices,  were  cleaned  and degreased and have carefully studied the state of cutting edges.      The working surfaces of cutting dies, punching, bending, who had minor scratches and worn edges were reconditioned by rectification.      The restoring active profile and the initial sizes of the work item (active) that during the operation were blunted, broken and wasted was performed by applying a metal layer, after which it was cleaned and rectified at prescribed dimensions on the execution design of the reconditioned element.      Among the techniques used, especially for restoring the active elements in the work area are rectified frontal surfaces, hard chromating, hardening with electric sparks and charging welding.  3.  The rectification of the frontal surfaces.       The working surfaces of cutting dies, punching, showing minor scratches and worn edges were reconditioned by rectification.      The durability of dies depends on many factors such as durability itself, which is estimated by the number of work races, or using the number of items processed between two sharpening punch and plaque rectification of active, durability active elements of dies, estimated by the maximum  possible  active  race  (work)  until  they  are  replaced,  maximum  operating  dies, estimated by the maximum possible number of races to wear it all the active elements, they can not rehabilitate.               For calculation of cutting dies durability we used the relationship: pa D  = h/g where:  pa D  – represents the number of the active plaque reconditioning;     h – blade height active plaque;     g – the layer thickness of the removed material.      The cutting active plaque high is 3 mm, but the thickness of the away layer by rectification is 0,3mm. Result that  pa D =2,7/0,3=9. The lifetime of the active plaque until totally wear, is determined by the relation: fpa D  = (h/g + 1)DK      In which:  D – represents the itself durability(between two regrindings) 15000 strokes; K – coefficient reduction of the dies durability after each regrinding K = 0,9        Result that   fpa D =(9+1) 150000,9=135000 strokes.  4.  Reconditioning of electric sparks and hard chrome active of the edges.       These technologies have been presented in detail in Chapter 2, "Heat treatment applied to tool steels".      Reconditioning by covering by spark,  lend themselves to the tools with a less wear and   Fiabilitate si Durabilitate - Fiability & Durability    Supplement no 1/ 2012   Editura “Academica Brâncuşi” , Târgu Jiu, ISSN 1844 – 640X     216 reconditioning by hard chrome is used for tools with more wear.      The punch was removed from the press was opened and the die was cleaned of oil and impurities.      For  operation  of  hard  chrome  and  cover  spark  to  achieve  its  aims,  it  was  necessary rectified the used areas, removing the tread and the wear, so that chromium deposit to be uniform.      Deposited layers had equal depth of the cavities of edge tools, and hardness were for spark covered layer 755HV and 720HV for chrome layer.  5.  Reconditioning by welding load.       Reconditioning  by  welded  load  is  performed  to  increase  wear  resistance  and  toughness loading  dies  and  consists  in  working  load  edges  of  the  active  elements.  Shown  below reconditioning technology by welding a steel punch of OSC10 improved.      Before reconditioning punch was annealed for regeneration to change the structure of the constituents most compatible with welding. After regeneration, before starting the welding operation, process by pressing in active tool in the worn zone a hole and then preheated to a temperature of 550oC.       Later, the cavity was filled with weld by superposed layers. After loading the weld the piece  was  subjected  to  a  normalization  treatment.  After  adjustment  followed  by  heat treatments  of  burning  and  tempering  to  correspond  to  hardness  before  Reconditioning, followed by rectification prescribed profile. Final hardness was 61 HRC.      For charging welding electrodes were used 100CrMoV type. Welding operation was done with device continuous current with short arc reverse polarity, that the piece was connected to the negative pole and the electrode to the positive pole, this connection avoiding overheating.      The current intensity loading of the weld was 130 A, electrode diameter was 3 mm. The reconditioning by charging weld,the electrode was held at an angle position after contour waste area. However, to avoid cracks in the deposited layers, the core material was heated to annealing temperature softening and maintained in the temperature range 450 ... 550 C (to ensure maximum stability of austenitic constituent).      After  loading  the  welding  operation  followed  the  operation  for  adjusting  the  active elements after template for the smooth functioning of the dies. Adjustment of active edges was done after template at paint with a hand grinder, fitted with abrasive wheel of 46 grain. For final adjustment were used grinding wheels with different profiles, with a granule size 46-80 from synthetic corundum (electro-corundum) and bakelite binder.      After rectification with abrasive stone were cleaned asperities. The direction of movement of the abrasive stone was constant, for keeping active geometry.      Fixing surfaces were adjusted to the paint, after die cutting the semi around 600. After finishing the adjustment operation,the die sat again on the press for the settlement. Figure 3 presents a macro picture of the steel punch OSC10 reconditioned by welding.                                                                                    Fiabilitate si Durabilitate - Fiability & Durability    Supplement no 1/ 2012   Editura “Academica Brâncuşi” , Târgu Jiu, ISSN 1844 – 640X     217                                                                                       Area refurbished by welding                                                    Fig.3 Die OSC10 refurbished by welding    6.  Concluzions:       By applying reconditioning was increased the indicators so implicitly durability of cutting tools.      Were restored active profile and size of the work active elements so after reconditioning they  corresponded  in  terms  of  dimensional  precision  and  resistance  to  wear,  like  initial elements.      The condition of the active elements was verified after dimensional accuracy and form of the last pieces punched which was classified as tolerances and technical design requirements of its execution.   References  [1]  Stăncioiu  Alin,  Cercetări  cu  privire  la  influenţa  calităţii  sculelor  asupra  proceselor tehnologice de tăiere, Universitatea din Craiova, Teza de Doctorat, 2004 [2]  Şontea, Sever., Tratamente termice şi termochimice, Editura Spirit Românesc, Craiova, 2001 [3]  Şontea, Sever,Metale şi aliaje neferoase de turnătorie, Ed. Scrisul Românesc Craiova, 1981 

RESEARCH ON INCREASING ACTIVE LIFE OF CUTTING TOOLS

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