Looking at Castings Environmental Impact Across Their Life Cycles

交通运输部门约占全球能源相关二氧化碳排放量的23%，预计其增长速度将快于其他能源终端使用部门. To mitigate this impact, 汽车燃油经济性法规，如美国环保署的企业平均燃油经济性(CAFE)标准已被采用. While effective at improving fuel economy, 这些汽车法规仅限于减少尾气管中的二氧化碳和其他温室气体排放. Consequently, 这些法规忽略了由于生产汽车内部组件和回收或其他报废影响而产生的排放，这些影响可能导致车辆使用寿命期间温室气体排放的意外增加.

生命周期分析是一门相对较新的学科，它包含了所有主要阶段——生产阶段, 产品或过程生命周期的使用和回收/生命周期结束，以计算总影响. 它正迅速成为学术界和行业分析师的关键工具，甚至已开始在监管环境中使用. 欧盟委员会称生命周期思维是“评估产品潜在环境影响的最佳框架”, processes and systems.” Moreover, 欧盟已经有了直接基于生命周期分析的现有立法, 这需要计算生物燃料的生命周期温室气体排放量. Within the U.S., California has adopted a Low Carbon Fuel Standard. Furthermore, 业界已经存在许多适应生命周期分析的解决方案, such as open-source software 
and models.

生命周期分析在监管项目中的推广表明，类似的方法可能成为限制温室气体排放的首选计算方法. 柏林环境技术研究所(Institute of Environmental Technology)的研究人员已经起草了许多不同的流程选择，以便将其纳入政府政策, including those based on existing ISO standards. 
Due to their recyclability and lower embodied energy, castings have the potential to be more sustainable in this framework, but more data is needed to quantify the impact.

Castings and Life Cycle Analyses

广泛的文献回顾发现，只有有限数量的铸造相关的生命周期分析，包括使用阶段. 相反，大多数文献关注的是生产和回收过程中的能源和成本. 这包括铸铝和铸镁的两个生命周期库存数据库，提供生产和回收投入, which can aid future analysis containing all major phases.
While production and end-of-life impacts can inform producer decisions, 评估新材料的汽车供应商将会寻找整个生命周期的故事, as it is misleading to only report the production and end-of-life phases. In one example, 大众高尔夫VII车辆(驾驶20辆)全生命周期温室气体排放量的79%,000 km or 12,400 miles yearly) come from the use-phase. Even with the databases available for two major casting materials, only three studies were found that included all three phases––production, use and end-of-life––for cast components:

• “Primary Manufacturing, 发动机生产和道路二氧化碳:汽车工业如何为环境可持续性做出最大贡献?” 38th International Vienna Motor Symposium (April 2017).
• Jhaveri et al., 汽车轻量化应用薄壁球墨铸铁的生命周期评估,” Sustainable Materials and Technologies, Vol. 15, pp. 1–8 (2018).
• Simone Ehrenberger, “Life Cycle Assessment of Magnesium Components in Vehicle Construction,”  The International Magnesium Association (May 2013).

This list is almost certainly non-exhaustive, but it displays the lack of research into this topic for castings. Furthermore, 铸件生命周期分析工作的范围是有限的:这三种研究只比较了其他铸造工艺，而没有比较其他材料工艺. 

Arguments for Why Castings May Have a Lower Environmental Impact

Despite the lack of life cycle analysis research into castings, 几个貌似合理的原因解释了为什么铸件比其他形式的加工具有更低的生命周期能源和温室气体影响. 

In the production phase, 与使用相同材料的其他工艺相比，铸件每公斤的隐含能量更低. 1). 这很可能是因为铸件是从原材料到成品的最短路径. As a caveat, 而隐含能量并不等同于产品整个生命周期的温室气体排放, it is a significant component of life-cycle emissions. Consequently, assuming the same electrical sources, 在产品的整个生命周期内，隐含能量的减少也会导致温室气体排放的减少. 

During the use-phase, 对燃料消耗影响最大，因此对能源和温室气体排放影响最大, is vehicle weight. 由于金属铸造是一种接近净形的工艺，可以最大限度地减少机加工量, finishing, and number of parts per component, castings provide excellent opportunity for lightweighting. 

For example, as discussed in a recent Casting Source article, “3 Ways Vehicles Are Reducing Weight,” converting a steel stamping to a magnesium casting resulted in 19.4 lbs. of mass savings and part number consolidation (Fig. 2). In another example from the same article, 将铝冲压组件转换为铝铸件可节省20%的重量并整合零件编号(图1). 3). Part number consolidation may translate to cost-savings, 大量的节约将转化为使用阶段温室气体排放的减少.

As scrap metal accumulates from different metal processing streams, chemical impurities in the scrap become more concentrated. Due to the high-purity material specifications for wrought metals, 制造商不能使用大量的废料进行生产. This specification is not as strong for cast components. For instance, wrought aluminum can be recycled into cast aluminum components, but the reverse is unlikely. 最近的文献表明，锻造铝的基线二次含量值为0%, while they are 85% for cast aluminum. 同样，扁钢、长钢和铸钢的基准二次含量分别为5%、85%和100%. Because castings are inherently more recyclable, 在寿命结束阶段的能源和温室气体排放也会更低.

对于相同的基础材料，铸件比其他工艺更具有可持续性, even when lightweighting is not feasible. Because of castings’ edge in production and recyclability, 它们的生产仍然可以节省能源和温室气体排放，同时为汽车供应商提供低成本的解决方案. Ultimately, in a life cycle analysis-focused regulatory environment, 铸造行业可以合理地辩称，他们的工艺是最可持续的. However, to maximize the effectiveness of this argument, thorough castings life cycle analysis research is needed.