Science and Technology Three-dimensional printing An image of the future
科技3D印刷印刷未来
One of the biggest manufacturers in the world gives 3D printing a go
世界龙头机器制造商用3D印刷术进行了一次格外成功的应用
ULTRASOUND scanners are used for tasks as diverse as examining unborn babies and searching for cracks in the fabric of aircraft. They work by sending out pulses of high-frequency sound and then interpreting the reflections as images. To do all this, though, you need a device called a transducer.
超声波扫描器的应用领域很广，小到用于检查胎儿，大到飞行器机体瑕疵检测等。机理过程是，通过发射高频声波脉冲信号对反射信号进行成像解读。但完成该过程，你不能缺少一台叫做‘压电式换能器'的设备。
Transducers are made from arrays of tiny piezoelectric structures that convert electrical signals into ultrasound waves by vibrating at an appropriate frequency. Their shape focuses the waves so that they penetrate the object being scanned. The waves are then reflected back from areas where there is a change in density and on their return the transducer works in reverse, producing a signal which the scanner can process into a digital image.
压电式换能器是由具有‘压电'效应的一系列敏感元件机构组成。敏感元件机构通过‘定频'震荡将电信号转换成超声波。机构的特定外形可聚焦超声波，对被扫描的物体产生穿透作用。超声波会从密度发生变化的介质反射回来，这时压电式换能器会反向操作产生信号，再经过扫描器的处理，最后进行数字成像。
To make a transducer by painstakingly micro-machining a brittle block of ceramic material can take many hours of work, though. As a result, even as the size and cost of the console that controls the scanner has fallen with advances in microelectronics (some are now small enough to fit in a doctor's pocket and cost a few hundred dollars), the cost of making the probe itself remains stubbornly high—as much as ten times that of the console.
压电式换能器需要用到陶瓷材料，而精密地加工一块精细的陶瓷材料就要耗费几个小时的工作时间。随着微电子领域中，技术的突飞猛进，控制扫描仪的电路板无论从体积还有成本都有很大程度的优化变小和降低。有些电路板小到可以装进医生口袋里面，成本也不过几百美元的价格。而制作换能器探头的成本却一直居高不下，跟电路板相比，探头的制作成本大概是一块电路板的10倍左右。
At least, it does if you use traditional "subtractive" manufacturing techniques like cutting and drilling. However GE, a large American conglomerate, is now proposing to make ultrasound transducers by "additive" manufacturing—or three-dimensional printing, as it is also known. A new laboratory at the firm's research centre in Niskayuna, New York, is taking a hard-headed look
at the technique, which some see as a fad and others as the future, and working out which products might be made more efficiently by addition rather than subtraction.
即使不考虑体积及成本的情况下，传统的‘对比相减式'加工流程技术也能完成这些工作，比如切割，机钻等。而GE作为美国的一个庞大的企业集团正考虑采用‘对比添加式'的加工流程（或者又称大家所熟悉的‘3D印刷'）来加工超声波压电式换能器。GE在纽约Niskayuna地区的研发中心新成立了一个实验室，目前该实验室正本着理性实际的态度（非一时狂热）对该项技术进行研发，力图找到哪些产品用‘对比添加式'而非‘对比相减式'的技术流程加工生产更加适合，一些人认为，对该项技术的研发只不过是一时狂热。还有一些人声称，目前的时机并不成熟，对该项技术的研发仅仅具有‘将来时'的意义罢了。
Ultrasound transducers were an early pick both because of the complicated geometry needed to focus the sound waves and because ceramics are harder than metals to cut and drill accurately. But they are easy to print.
最初选择超声波压电式换能器来作为‘3D印刷术'的对象原因有两点。一是该换能器用来聚焦声波的机体外形非常复杂，二是它用到的陶瓷材料比金属的硬度要高很多，很难进行精准地切割和机钻。而用‘3D印刷术'却很容易解决这两个难题。
The GE process for making a transducer begins by spreading onto the print table a thin layer of ceramic slurry containing a light-sensitive polymer. This layer is exposed to ultraviolet light through a mask that represents the required pattern. Wherever the light falls on the polymer it causes it to solidify, binding the particles in the slurry together.
GE对加工换能器的方法是首先在印刷台上撒上薄薄的一层陶瓷粘土，其中混入一种光敏聚合体。然后用紫外线通过露光模板的光孔照射到印刷台的粘土层，以此塑造出需要的模型图案。光敏聚合体一经被紫外线照射就会立即变得坚硬，粘土中的粒子随即凝结固化。
The print table is then lowered by a fraction of a millimetre and the process repeated, with a different mask if required. And so on. Once finished, the solidified shape is cleaned of residual slurry and heated in a furnace to sinter the ceramic particles together. More work will be needed to turn the process into a production-ready system. But Prabhjot Singh, who leads the project, hopes that it will be possible to use it to make not just cheaper ultrasound probes, but also more sensitive ones that can show greater detail. Although researchers have had new transducer designs in mind for years, it has been impractical to construct them subtractively. Additive manufacturing could change that.
接下来，印刷台会以不超过一毫米的距离向下位移，然后重复整个上面这一过程，如果有必要，需要重新更换一个新的露光模板。以此反复处理直到整个过程结束，再进行清理成模上的残余粘土，最后把成模放入熔炉，以低于熔点的温度进行焙烧，最终完成陶瓷粒子的凝固收缩聚合。该处理流程在具有批量生产体系能力之前，还需要做很多的工作。但项目负责人Prabhjot Singh表示，希望不仅仅制造出成本相对低廉的超声波探头，最好探头的灵敏性也会更高，这样可以让我们通过成像看到更加细节化的信息。多年以来，压电式换能器的研究者们一直都有新型设计的想法，但应用‘对比相减式'的加工流程实际上很难能把这
