In the grinding of high quality fused silica parts with complex surface or structure using ball-headed metal bonded diamond wheel with small diameter,the existing dressing methods are not suitable to dress the ball-he...In the grinding of high quality fused silica parts with complex surface or structure using ball-headed metal bonded diamond wheel with small diameter,the existing dressing methods are not suitable to dress the ball-headed diamond wheel precisely due to that they are either on-line in process dressing which may causes collision problem or without consideration for the effects of the tool setting error and electrode wear.An on-machine precision preparation and dressing method is proposed for ball-headed diamond wheel based on electrical discharge machining.By using this method the cylindrical diamond wheel with small diameter is manufactured to hemispherical-headed form.The obtained ball-headed diamond wheel is dressed after several grinding passes to recover geometrical accuracy and sharpness which is lost due to the wheel wear.A tool setting method based on high precision optical system is presented to reduce the wheel center setting error and dimension error.The effect of electrode tool wear is investigated by electrical dressing experiments,and the electrode tool wear compensation model is established based on the experimental results which show that the value of wear ratio coefficient K’ tends to be constant with the increasing of the feed length of electrode and the mean value of K’ is 0.156.Grinding experiments of fused silica are carried out on a test bench to evaluate the performance of the preparation and dressing method.The experimental results show that the surface roughness of the finished workpiece is 0.03 μm.The effect of the grinding parameter and dressing frequency on the surface roughness is investigated based on the measurement results of the surface roughness.This research provides an on-machine preparation and dressing method for ball-headed metal bonded diamond wheel used in the grinding of fused silica,which provides a solution to the tool setting method and the effect of electrode tool wear.展开更多
Purpose: Closed head injuries are more common than penetrating head injuries in our clinical practices. Penetrating head injuries can be happened in industrial accidents, car accidents, fall accidents or criminal acti...Purpose: Closed head injuries are more common than penetrating head injuries in our clinical practices. Penetrating head injuries can be happened in industrial accidents, car accidents, fall accidents or criminal activities, also they can be occurred in self-inflicted injuries. We reported a case of self-inflicted penetrating head injury to highlight the importance of suicide precaution and review the principle of management of penetrating head injury. Methods and Results: A 58 year-old woman, who has hypertension and major depression, attempted suicide by inserting a ball-pen into her brain through the right temple in the psychiatric ward. CT of brain showed a foreign body penetrating through the right sphenoid ridge to intracranial right frontal-temporal junction, right parasella and suprasella cistern to interpeduncular cistern and acute subarachnoid hemorrhage in the basal cistern and right sylvian fissure. She underwent an emergent neurosurgical procedure to remove the ball-pen, to evacuate the intracranial hematoma and to repair the lacerated dura. She recovered gradually and was clear after surgery, but a right oculomotor palsy and very mild left hemiparesis were left. Discussion: We learn a lesson from this patient, even a ball-pen can become a weapon in the hands of depression patients. All clinicians should be aware of the psychological condition of each patient and suicide precaution should be kept in mind in clinical practice.展开更多
基金supported by National Natural Science Foundation of China(Grant No.50935003)National Numerical Control Major Projects of China(Grant No.2013ZX04001000-215)
文摘In the grinding of high quality fused silica parts with complex surface or structure using ball-headed metal bonded diamond wheel with small diameter,the existing dressing methods are not suitable to dress the ball-headed diamond wheel precisely due to that they are either on-line in process dressing which may causes collision problem or without consideration for the effects of the tool setting error and electrode wear.An on-machine precision preparation and dressing method is proposed for ball-headed diamond wheel based on electrical discharge machining.By using this method the cylindrical diamond wheel with small diameter is manufactured to hemispherical-headed form.The obtained ball-headed diamond wheel is dressed after several grinding passes to recover geometrical accuracy and sharpness which is lost due to the wheel wear.A tool setting method based on high precision optical system is presented to reduce the wheel center setting error and dimension error.The effect of electrode tool wear is investigated by electrical dressing experiments,and the electrode tool wear compensation model is established based on the experimental results which show that the value of wear ratio coefficient K’ tends to be constant with the increasing of the feed length of electrode and the mean value of K’ is 0.156.Grinding experiments of fused silica are carried out on a test bench to evaluate the performance of the preparation and dressing method.The experimental results show that the surface roughness of the finished workpiece is 0.03 μm.The effect of the grinding parameter and dressing frequency on the surface roughness is investigated based on the measurement results of the surface roughness.This research provides an on-machine preparation and dressing method for ball-headed metal bonded diamond wheel used in the grinding of fused silica,which provides a solution to the tool setting method and the effect of electrode tool wear.
文摘Purpose: Closed head injuries are more common than penetrating head injuries in our clinical practices. Penetrating head injuries can be happened in industrial accidents, car accidents, fall accidents or criminal activities, also they can be occurred in self-inflicted injuries. We reported a case of self-inflicted penetrating head injury to highlight the importance of suicide precaution and review the principle of management of penetrating head injury. Methods and Results: A 58 year-old woman, who has hypertension and major depression, attempted suicide by inserting a ball-pen into her brain through the right temple in the psychiatric ward. CT of brain showed a foreign body penetrating through the right sphenoid ridge to intracranial right frontal-temporal junction, right parasella and suprasella cistern to interpeduncular cistern and acute subarachnoid hemorrhage in the basal cistern and right sylvian fissure. She underwent an emergent neurosurgical procedure to remove the ball-pen, to evacuate the intracranial hematoma and to repair the lacerated dura. She recovered gradually and was clear after surgery, but a right oculomotor palsy and very mild left hemiparesis were left. Discussion: We learn a lesson from this patient, even a ball-pen can become a weapon in the hands of depression patients. All clinicians should be aware of the psychological condition of each patient and suicide precaution should be kept in mind in clinical practice.
